Mailman 3 September 2008 - Python-Dev

PEP 1, PEP Purpose and Guidelines
by barry＠zope.com May 18, 2021

May 18, 2021

It has been a while since I posted a copy of PEP 1 to the mailing lists and newsgroups. I've recently done some updating of a few sections, so in the interest of gaining wider community participation in the Python development process, I'm posting the latest revision of PEP 1 here. A version of the PEP is always available on-line at http://www.python.org/peps/pep-0001.html Enjoy, -Barry -------------------- snip snip -------------------- PEP: 1 Title: PEP Purpose and Guidelines Version: $Revision: 1.36 $ Last-Modified: $Date: 2002/07/29 18:34:59 $ Author: Barry A. Warsaw, Jeremy Hylton Status: Active Type: Informational Created: 13-Jun-2000 Post-History: 21-Mar-2001, 29-Jul-2002 What is a PEP? PEP stands for Python Enhancement Proposal. A PEP is a design document providing information to the Python community, or describing a new feature for Python. The PEP should provide a concise technical specification of the feature and a rationale for the feature. We intend PEPs to be the primary mechanisms for proposing new features, for collecting community input on an issue, and for documenting the design decisions that have gone into Python. The PEP author is responsible for building consensus within the community and documenting dissenting opinions. Because the PEPs are maintained as plain text files under CVS control, their revision history is the historical record of the feature proposal[1]. Kinds of PEPs There are two kinds of PEPs. A standards track PEP describes a new feature or implementation for Python. An informational PEP describes a Python design issue, or provides general guidelines or information to the Python community, but does not propose a new feature. Informational PEPs do not necessarily represent a Python community consensus or recommendation, so users and implementors are free to ignore informational PEPs or follow their advice. PEP Work Flow The PEP editor, Barry Warsaw <peps(a)python.org>, assigns numbers for each PEP and changes its status. The PEP process begins with a new idea for Python. It is highly recommended that a single PEP contain a single key proposal or new idea. The more focussed the PEP, the more successfully it tends to be. The PEP editor reserves the right to reject PEP proposals if they appear too unfocussed or too broad. If in doubt, split your PEP into several well-focussed ones. Each PEP must have a champion -- someone who writes the PEP using the style and format described below, shepherds the discussions in the appropriate forums, and attempts to build community consensus around the idea. The PEP champion (a.k.a. Author) should first attempt to ascertain whether the idea is PEP-able. Small enhancements or patches often don't need a PEP and can be injected into the Python development work flow with a patch submission to the SourceForge patch manager[2] or feature request tracker[3]. The PEP champion then emails the PEP editor <peps(a)python.org> with a proposed title and a rough, but fleshed out, draft of the PEP. This draft must be written in PEP style as described below. If the PEP editor approves, he will assign the PEP a number, label it as standards track or informational, give it status 'draft', and create and check-in the initial draft of the PEP. The PEP editor will not unreasonably deny a PEP. Reasons for denying PEP status include duplication of effort, being technically unsound, not providing proper motivation or addressing backwards compatibility, or not in keeping with the Python philosophy. The BDFL (Benevolent Dictator for Life, Guido van Rossum) can be consulted during the approval phase, and is the final arbitrator of the draft's PEP-ability. If a pre-PEP is rejected, the author may elect to take the pre-PEP to the comp.lang.python newsgroup (a.k.a. python-list(a)python.org mailing list) to help flesh it out, gain feedback and consensus from the community at large, and improve the PEP for re-submission. The author of the PEP is then responsible for posting the PEP to the community forums, and marshaling community support for it. As updates are necessary, the PEP author can check in new versions if they have CVS commit permissions, or can email new PEP versions to the PEP editor for committing. Standards track PEPs consists of two parts, a design document and a reference implementation. The PEP should be reviewed and accepted before a reference implementation is begun, unless a reference implementation will aid people in studying the PEP. Standards Track PEPs must include an implementation - in the form of code, patch, or URL to same - before it can be considered Final. PEP authors are responsible for collecting community feedback on a PEP before submitting it for review. A PEP that has not been discussed on python-list(a)python.org and/or python-dev(a)python.org will not be accepted. However, wherever possible, long open-ended discussions on public mailing lists should be avoided. Strategies to keep the discussions efficient include, setting up a separate SIG mailing list for the topic, having the PEP author accept private comments in the early design phases, etc. PEP authors should use their discretion here. Once the authors have completed a PEP, they must inform the PEP editor that it is ready for review. PEPs are reviewed by the BDFL and his chosen consultants, who may accept or reject a PEP or send it back to the author(s) for revision. Once a PEP has been accepted, the reference implementation must be completed. When the reference implementation is complete and accepted by the BDFL, the status will be changed to `Final.' A PEP can also be assigned status `Deferred.' The PEP author or editor can assign the PEP this status when no progress is being made on the PEP. Once a PEP is deferred, the PEP editor can re-assign it to draft status. A PEP can also be `Rejected'. Perhaps after all is said and done it was not a good idea. It is still important to have a record of this fact. PEPs can also be replaced by a different PEP, rendering the original obsolete. This is intended for Informational PEPs, where version 2 of an API can replace version 1. PEP work flow is as follows: Draft -> Accepted -> Final -> Replaced ^ +----> Rejected v Deferred Some informational PEPs may also have a status of `Active' if they are never meant to be completed. E.g. PEP 1. What belongs in a successful PEP? Each PEP should have the following parts: 1. Preamble -- RFC822 style headers containing meta-data about the PEP, including the PEP number, a short descriptive title (limited to a maximum of 44 characters), the names, and optionally the contact info for each author, etc. 2. Abstract -- a short (~200 word) description of the technical issue being addressed. 3. Copyright/public domain -- Each PEP must either be explicitly labelled as placed in the public domain (see this PEP as an example) or licensed under the Open Publication License[4]. 4. Specification -- The technical specification should describe the syntax and semantics of any new language feature. The specification should be detailed enough to allow competing, interoperable implementations for any of the current Python platforms (CPython, JPython, Python .NET). 5. Motivation -- The motivation is critical for PEPs that want to change the Python language. It should clearly explain why the existing language specification is inadequate to address the problem that the PEP solves. PEP submissions without sufficient motivation may be rejected outright. 6. Rationale -- The rationale fleshes out the specification by describing what motivated the design and why particular design decisions were made. It should describe alternate designs that were considered and related work, e.g. how the feature is supported in other languages. The rationale should provide evidence of consensus within the community and discuss important objections or concerns raised during discussion. 7. Backwards Compatibility -- All PEPs that introduce backwards incompatibilities must include a section describing these incompatibilities and their severity. The PEP must explain how the author proposes to deal with these incompatibilities. PEP submissions without a sufficient backwards compatibility treatise may be rejected outright. 8. Reference Implementation -- The reference implementation must be completed before any PEP is given status 'Final,' but it need not be completed before the PEP is accepted. It is better to finish the specification and rationale first and reach consensus on it before writing code. The final implementation must include test code and documentation appropriate for either the Python language reference or the standard library reference. PEP Template PEPs are written in plain ASCII text, and should adhere to a rigid style. There is a Python script that parses this style and converts the plain text PEP to HTML for viewing on the web[5]. PEP 9 contains a boilerplate[7] template you can use to get started writing your PEP. Each PEP must begin with an RFC822 style header preamble. The headers must appear in the following order. Headers marked with `*' are optional and are described below. All other headers are required. PEP: <pep number> Title: <pep title> Version: <cvs version string> Last-Modified: <cvs date string> Author: <list of authors' real names and optionally, email addrs> * Discussions-To: <email address> Status: <Draft | Active | Accepted | Deferred | Final | Replaced> Type: <Informational | Standards Track> * Requires: <pep numbers> Created: <date created on, in dd-mmm-yyyy format> * Python-Version: <version number> Post-History: <dates of postings to python-list and python-dev> * Replaces: <pep number> * Replaced-By: <pep number> The Author: header lists the names and optionally, the email addresses of all the authors/owners of the PEP. The format of the author entry should be address(a)dom.ain (Random J. User) if the email address is included, and just Random J. User if the address is not given. If there are multiple authors, each should be on a separate line following RFC 822 continuation line conventions. Note that personal email addresses in PEPs will be obscured as a defense against spam harvesters. Standards track PEPs must have a Python-Version: header which indicates the version of Python that the feature will be released with. Informational PEPs do not need a Python-Version: header. While a PEP is in private discussions (usually during the initial Draft phase), a Discussions-To: header will indicate the mailing list or URL where the PEP is being discussed. No Discussions-To: header is necessary if the PEP is being discussed privately with the author, or on the python-list or python-dev email mailing lists. Note that email addresses in the Discussions-To: header will not be obscured. Created: records the date that the PEP was assigned a number, while Post-History: is used to record the dates of when new versions of the PEP are posted to python-list and/or python-dev. Both headers should be in dd-mmm-yyyy format, e.g. 14-Aug-2001. PEPs may have a Requires: header, indicating the PEP numbers that this PEP depends on. PEPs may also have a Replaced-By: header indicating that a PEP has been rendered obsolete by a later document; the value is the number of the PEP that replaces the current document. The newer PEP must have a Replaces: header containing the number of the PEP that it rendered obsolete. PEP Formatting Requirements PEP headings must begin in column zero and the initial letter of each word must be capitalized as in book titles. Acronyms should be in all capitals. The body of each section must be indented 4 spaces. Code samples inside body sections should be indented a further 4 spaces, and other indentation can be used as required to make the text readable. You must use two blank lines between the last line of a section's body and the next section heading. You must adhere to the Emacs convention of adding two spaces at the end of every sentence. You should fill your paragraphs to column 70, but under no circumstances should your lines extend past column 79. If your code samples spill over column 79, you should rewrite them. Tab characters must never appear in the document at all. A PEP should include the standard Emacs stanza included by example at the bottom of this PEP. A PEP must contain a Copyright section, and it is strongly recommended to put the PEP in the public domain. When referencing an external web page in the body of a PEP, you should include the title of the page in the text, with a footnote reference to the URL. Do not include the URL in the body text of the PEP. E.g. Refer to the Python Language web site [1] for more details. ... [1] http://www.python.org When referring to another PEP, include the PEP number in the body text, such as "PEP 1". The title may optionally appear. Add a footnote reference that includes the PEP's title and author. It may optionally include the explicit URL on a separate line, but only in the References section. Note that the pep2html.py script will calculate URLs automatically, e.g.: ... Refer to PEP 1 [7] for more information about PEP style ... References [7] PEP 1, PEP Purpose and Guidelines, Warsaw, Hylton http://www.python.org/peps/pep-0001.html If you decide to provide an explicit URL for a PEP, please use this as the URL template: http://www.python.org/peps/pep-xxxx.html PEP numbers in URLs must be padded with zeros from the left, so as to be exactly 4 characters wide, however PEP numbers in text are never padded. Reporting PEP Bugs, or Submitting PEP Updates How you report a bug, or submit a PEP update depends on several factors, such as the maturity of the PEP, the preferences of the PEP author, and the nature of your comments. For the early draft stages of the PEP, it's probably best to send your comments and changes directly to the PEP author. For more mature, or finished PEPs you may want to submit corrections to the SourceForge bug manager[6] or better yet, the SourceForge patch manager[2] so that your changes don't get lost. If the PEP author is a SF developer, assign the bug/patch to him, otherwise assign it to the PEP editor. When in doubt about where to send your changes, please check first with the PEP author and/or PEP editor. PEP authors who are also SF committers, can update the PEPs themselves by using "cvs commit" to commit their changes. Remember to also push the formatted PEP text out to the web by doing the following: % python pep2html.py -i NUM where NUM is the number of the PEP you want to push out. See % python pep2html.py --help for details. Transferring PEP Ownership It occasionally becomes necessary to transfer ownership of PEPs to a new champion. In general, we'd like to retain the original author as a co-author of the transferred PEP, but that's really up to the original author. A good reason to transfer ownership is because the original author no longer has the time or interest in updating it or following through with the PEP process, or has fallen off the face of the 'net (i.e. is unreachable or not responding to email). A bad reason to transfer ownership is because you don't agree with the direction of the PEP. We try to build consensus around a PEP, but if that's not possible, you can always submit a competing PEP. If you are interested assuming ownership of a PEP, send a message asking to take over, addressed to both the original author and the PEP editor <peps(a)python.org>. If the original author doesn't respond to email in a timely manner, the PEP editor will make a unilateral decision (it's not like such decisions can be reversed. :). References and Footnotes [1] This historical record is available by the normal CVS commands for retrieving older revisions. For those without direct access to the CVS tree, you can browse the current and past PEP revisions via the SourceForge web site at http://cvs.sourceforge.net/cgi-bin/cvsweb.cgi/python/nondist/peps/?cvsroot=… [2] http://sourceforge.net/tracker/?group_id=5470&atid=305470 [3] http://sourceforge.net/tracker/?atid=355470&group_id=5470&func=browse [4] http://www.opencontent.org/openpub/ [5] The script referred to here is pep2html.py, which lives in the same directory in the CVS tree as the PEPs themselves. Try "pep2html.py --help" for details. The URL for viewing PEPs on the web is http://www.python.org/peps/ [6] http://sourceforge.net/tracker/?group_id=5470&atid=305470 [7] PEP 9, Sample PEP Template http://www.python.org/peps/pep-0009.html Copyright This document has been placed in the public domain. Local Variables: mode: indented-text indent-tabs-mode: nil sentence-end-double-space: t fill-column: 70 End:

8 14

pthreads, fork, import, and execvp
by Rotem Yaari Sept. 16, 2009

Sept. 16, 2009

Hello everyone! We have been encountering several deadlocks in a threaded Python application which calls subprocess.Popen (i.e. fork()) in some of its threads. This has occurred on Python 2.4.1 on a 2.4.27 Linux kernel. Preliminary analysis of the hang shows that the child process blocks upon entering the execvp function, in which the import_lock is acquired due to the following line: def _ execvpe(file, args, env=None): from errno import ENOENT, ENOTDIR ... It is known that when forking from a pthreaded application, acquisition attempts on locks which were already locked by other threads while fork() was called will deadlock. Due to these oddities we were wondering if it would be better to extract the above import line from the execvpe call, to prevent lock acquisition attempts in such cases. Another workaround could be re-assigning a new lock to import_lock (such a thing is done with the global interpreter lock) at PyOS_AfterFork or pthread_atfork. We'd appreciate any opinions you might have on the subject. Thanks in advance, Yair and Rotem

12 29

Re: subprocess and EINTR errnos
by Peter Astrand July 6, 2009

July 6, 2009

On Wed, 10 Nov 2004, John P Speno wrote: Hi, sorry for the delayed response. > While using subprocess (aka popen5), I came across one potential gotcha. I've had > exceptions ending like this: > > File "test.py", line 5, in test > cmd = popen5.Popen(args, stdout=PIPE) > File "popen5.py", line 577, in __init__ > data = os.read(errpipe_read, 1048576) # Exceptions limited to 1 MB > OSError: [Errno 4] Interrupted system call > > (on Solaris 9) > > Would it make sense for subprocess to use a more robust read() function > which can handle these cases, i.e. when the parent's read on the pipe > to the child's stderr is interrupted by a system call, and returns EINTR? > I imagine it could catch EINTR and EAGAIN and retry the failed read(). I assume you are using signals in your application? The os.read above is not the only system call that can fail with EINTR. subprocess.py is full of other system calls that can fail, and I suspect that many other Python modules are as well. I've made a patch (attached) to subprocess.py (and test_subprocess.py) that should guard against EINTR, but I haven't committed it yet. It's quite large. Are Python modules supposed to handle EINTR? Why not let the C code handle this? Or, perhaps the signal module should provide a sigaction function, so that users can use SA_RESTART. Index: subprocess.py =================================================================== RCS file: /cvsroot/python/python/dist/src/Lib/subprocess.py,v retrieving revision 1.8 diff -u -r1.8 subprocess.py --- subprocess.py 7 Nov 2004 14:30:34 -0000 1.8 +++ subprocess.py 17 Nov 2004 19:42:30 -0000 @@ -888,6 +888,50 @@ pass + def _read_no_intr(self, fd, buffersize): + """Like os.read, but retries on EINTR""" + while True: + try: + return os.read(fd, buffersize) + except OSError, e: + if e.errno == errno.EINTR: + continue + else: + raise + + + def _read_all(self, fd, buffersize): + """Like os.read, but retries on EINTR, and reads until EOF""" + all = "" + while True: + data = self._read_no_intr(fd, buffersize) + all += data + if data == "": + return all + + + def _write_no_intr(self, fd, s): + """Like os.write, but retries on EINTR""" + while True: + try: + return os.write(fd, s) + except OSError, e: + if e.errno == errno.EINTR: + continue + else: + raise + + def _waitpid_no_intr(self, pid, options): + """Like os.waitpid, but retries on EINTR""" + while True: + try: + return os.waitpid(pid, options) + except OSError, e: + if e.errno == errno.EINTR: + continue + else: + raise + def _execute_child(self, args, executable, preexec_fn, close_fds, cwd, env, universal_newlines, startupinfo, creationflags, shell, @@ -963,7 +1007,7 @@ exc_value, tb) exc_value.child_traceback = ''.join(exc_lines) - os.write(errpipe_write, pickle.dumps(exc_value)) + self._write_no_intr(errpipe_write, pickle.dumps(exc_value)) # This exitcode won't be reported to applications, so it # really doesn't matter what we return. @@ -979,7 +1023,7 @@ os.close(errwrite) # Wait for exec to fail or succeed; possibly raising exception - data = os.read(errpipe_read, 1048576) # Exceptions limited to 1 MB + data = self._read_all(errpipe_read, 1048576) # Exceptions limited to 1 MB os.close(errpipe_read) if data != "": child_exception = pickle.loads(data) @@ -1003,7 +1047,7 @@ attribute.""" if self.returncode == None: try: - pid, sts = os.waitpid(self.pid, os.WNOHANG) + pid, sts = self._waitpid_no_intr(self.pid, os.WNOHANG) if pid == self.pid: self._handle_exitstatus(sts) except os.error: @@ -1015,7 +1059,7 @@ """Wait for child process to terminate. Returns returncode attribute.""" if self.returncode == None: - pid, sts = os.waitpid(self.pid, 0) + pid, sts = self._waitpid_no_intr(self.pid, 0) self._handle_exitstatus(sts) return self.returncode @@ -1049,27 +1093,33 @@ stderr = [] while read_set or write_set: - rlist, wlist, xlist = select.select(read_set, write_set, []) + try: + rlist, wlist, xlist = select.select(read_set, write_set, []) + except select.error, e: + if e[0] == errno.EINTR: + continue + else: + raise if self.stdin in wlist: # When select has indicated that the file is writable, # we can write up to PIPE_BUF bytes without risk # blocking. POSIX defines PIPE_BUF >= 512 - bytes_written = os.write(self.stdin.fileno(), input[:512]) + bytes_written = self._write_no_intr(self.stdin.fileno(), input[:512]) input = input[bytes_written:] if not input: self.stdin.close() write_set.remove(self.stdin) if self.stdout in rlist: - data = os.read(self.stdout.fileno(), 1024) + data = self._read_no_intr(self.stdout.fileno(), 1024) if data == "": self.stdout.close() read_set.remove(self.stdout) stdout.append(data) if self.stderr in rlist: - data = os.read(self.stderr.fileno(), 1024) + data = self._read_no_intr(self.stderr.fileno(), 1024) if data == "": self.stderr.close() read_set.remove(self.stderr) Index: test/test_subprocess.py =================================================================== RCS file: /cvsroot/python/python/dist/src/Lib/test/test_subprocess.py,v retrieving revision 1.14 diff -u -r1.14 test_subprocess.py --- test/test_subprocess.py 12 Nov 2004 15:51:48 -0000 1.14 +++ test/test_subprocess.py 17 Nov 2004 19:42:30 -0000 @@ -7,6 +7,7 @@ import tempfile import time import re +import errno mswindows = (sys.platform == "win32") @@ -35,6 +36,16 @@ fname = tempfile.mktemp() return os.open(fname, os.O_RDWR|os.O_CREAT), fname + def read_no_intr(self, obj): + while True: + try: + return obj.read() + except IOError, e: + if e.errno == errno.EINTR: + continue + else: + raise + # # Generic tests # @@ -123,7 +134,7 @@ p = subprocess.Popen([sys.executable, "-c", 'import sys; sys.stdout.write("orange")'], stdout=subprocess.PIPE) - self.assertEqual(p.stdout.read(), "orange") + self.assertEqual(self.read_no_intr(p.stdout), "orange") def test_stdout_filedes(self): # stdout is set to open file descriptor @@ -151,7 +162,7 @@ p = subprocess.Popen([sys.executable, "-c", 'import sys; sys.stderr.write("strawberry")'], stderr=subprocess.PIPE) - self.assertEqual(remove_stderr_debug_decorations(p.stderr.read()), + self.assertEqual(remove_stderr_debug_decorations(self.read_no_intr(p.stderr)), "strawberry") def test_stderr_filedes(self): @@ -186,7 +197,7 @@ 'sys.stderr.write("orange")'], stdout=subprocess.PIPE, stderr=subprocess.STDOUT) - output = p.stdout.read() + output = self.read_no_intr(p.stdout) stripped = remove_stderr_debug_decorations(output) self.assertEqual(stripped, "appleorange") @@ -220,7 +231,7 @@ stdout=subprocess.PIPE, cwd=tmpdir) normcase = os.path.normcase - self.assertEqual(normcase(p.stdout.read()), normcase(tmpdir)) + self.assertEqual(normcase(self.read_no_intr(p.stdout)), normcase(tmpdir)) def test_env(self): newenv = os.environ.copy() @@ -230,7 +241,7 @@ 'sys.stdout.write(os.getenv("FRUIT"))'], stdout=subprocess.PIPE, env=newenv) - self.assertEqual(p.stdout.read(), "orange") + self.assertEqual(self.read_no_intr(p.stdout), "orange") def test_communicate(self): p = subprocess.Popen([sys.executable, "-c", @@ -305,7 +316,8 @@ 'sys.stdout.write("\\nline6");'], stdout=subprocess.PIPE, universal_newlines=1) - stdout = p.stdout.read() + + stdout = self.read_no_intr(p.stdout) if hasattr(open, 'newlines'): # Interpreter with universal newline support self.assertEqual(stdout, @@ -343,7 +355,7 @@ def test_no_leaking(self): # Make sure we leak no resources - max_handles = 1026 # too much for most UNIX systems + max_handles = 10 # too much for most UNIX systems if mswindows: max_handles = 65 # a full test is too slow on Windows for i in range(max_handles): @@ -424,7 +436,7 @@ 'sys.stdout.write(os.getenv("FRUIT"))'], stdout=subprocess.PIPE, preexec_fn=lambda: os.putenv("FRUIT", "apple")) - self.assertEqual(p.stdout.read(), "apple") + self.assertEqual(self.read_no_intr(p.stdout), "apple") def test_args_string(self): # args is a string @@ -457,7 +469,7 @@ p = subprocess.Popen(["echo $FRUIT"], shell=1, stdout=subprocess.PIPE, env=newenv) - self.assertEqual(p.stdout.read().strip(), "apple") + self.assertEqual(self.read_no_intr(p.stdout).strip(), "apple") def test_shell_string(self): # Run command through the shell (string) @@ -466,7 +478,7 @@ p = subprocess.Popen("echo $FRUIT", shell=1, stdout=subprocess.PIPE, env=newenv) - self.assertEqual(p.stdout.read().strip(), "apple") + self.assertEqual(self.read_no_intr(p.stdout).strip(), "apple") def test_call_string(self): # call() function with string argument on UNIX @@ -525,7 +537,7 @@ p = subprocess.Popen(["set"], shell=1, stdout=subprocess.PIPE, env=newenv) - self.assertNotEqual(p.stdout.read().find("physalis"), -1) + self.assertNotEqual(self.read_no_intr(p.stdout).find("physalis"), -1) def test_shell_string(self): # Run command through the shell (string) @@ -534,7 +546,7 @@ p = subprocess.Popen("set", shell=1, stdout=subprocess.PIPE, env=newenv) - self.assertNotEqual(p.stdout.read().find("physalis"), -1) + self.assertNotEqual(self.read_no_intr(p.stdout).find("physalis"), -1) def test_call_string(self): # call() function with string argument on Windows /Peter Åstrand <astrand(a)lysator.liu.se>

5 5

deprecating BaseException.message
by Brett Cannon April 7, 2009

April 7, 2009

During the PyCon sprint I tried to make BaseException accept only a single argument and bind it to BaseException.message . I was successful (see the p3yk_no_args_on_exc branch), but it was very painful to pull off as anyone who sat around me the last three days of the sprint will tell you as they had to listen to me curse incessantly. Because of the pain that I went through in the transition and thus the lessons learned, Guido and I discussed it and we think it would be best to give up on forcing BaseException to accept only a single argument. I think it is still doable, but requires a multi-release transition period and not the one that 2.6 -> 3.0 is offering. And so Guido and I plan on deprecating BaseException.message as its entire point in existence was to help transition to what we are not going to have happen. =) Now that means BaseException.message might hold the record for shortest lived feature as it was only introduced in 2.5 and is now to be deprecated in 2.6 and removed in 2.7/3.0. =) Below is PEP 352, revised to reflect the removal of BaseException.messageand for letting the 'args' attribute stay (along with suggesting one should only pass a single argument to BaseException). Basically the interface for exceptions doesn't really change in 3.0 except for the removal of __getitem__. -------------------------------------------------------------------------- PEP: 352 Title: Required Superclass for Exceptions Version: $Revision: 53592 $ Last-Modified: $Date: 2007-01-28 21:54:11 -0800 (Sun, 28 Jan 2007) $ Author: Brett Cannon <brett(a)python.org> Guido van Rossum <guido(a)python.org> Status: Final Type: Standards Track Content-Type: text/x-rst Created: 27-Oct-2005 Post-History: Abstract ======== In Python 2.4 and before, any (classic) class can be raised as an exception. The plan for 2.5 was to allow new-style classes, but this makes the problem worse -- it would mean *any* class (or instance) can be raised! This is a problem as it prevents any guarantees from being made about the interface of exceptions. This PEP proposes introducing a new superclass that all raised objects must inherit from. Imposing the restriction will allow a standard interface for exceptions to exist that can be relied upon. It also leads to a known hierarchy for all exceptions to adhere to. One might counter that requiring a specific base class for a particular interface is unPythonic. However, in the specific case of exceptions there's a good reason (which has generally been agreed to on python-dev): requiring hierarchy helps code that wants to *catch* exceptions by making it possible to catch *all* exceptions explicitly by writing ``except BaseException:`` instead of ``except *:``. [#hierarchy-good]_ Introducing a new superclass for exceptions also gives us the chance to rearrange the exception hierarchy slightly for the better. As it currently stands, all exceptions in the built-in namespace inherit from Exception. This is a problem since this includes two exceptions (KeyboardInterrupt and SystemExit) that often need to be excepted from the application's exception handling: the default behavior of shutting the interpreter down without a traceback is usually more desirable than whatever the application might do (with the possible exception of applications that emulate Python's interactive command loop with ``>>>`` prompt). Changing it so that these two exceptions inherit from the common superclass instead of Exception will make it easy for people to write ``except`` clauses that are not overreaching and not catch exceptions that should propagate up. This PEP is based on previous work done for PEP 348 [#pep348]_. Requiring a Common Superclass ============================= This PEP proposes introducing a new exception named BaseException that is a new-style class and has a single attribute, ``args``. Below is the code as the exception will work in Python 3.0 (how it will work in Python 2.x is covered in the `Transition Plan`_ section):: class BaseException(object): """Superclass representing the base of the exception hierarchy. Provides a 'message' attribute that contains either the single argument to the constructor or the empty string. This attribute is used in the string representation for the exception. This is so that it provides the extra details in the traceback. """ def __init__(self, *args): """Set the 'message' attribute'""" self.args = args def __str__(self): """Return the str of 'message'""" if len(self.args) == 1: return str(self.args[0]) else: return str(self.args) def __repr__(self): return "%s(*%s)" % (self.__class__.__name__, repr(self.args)) No restriction is placed upon what may be passed in for ``args`` for backwards-compatibility reasons. In practice, though, only a single string argument should be used. This keeps the string representation of the exception to be a useful message about the exception that is human-readable; this is why the ``__str__`` method special-cases on length-1 ``args`` value. Including programmatic information (e.g., an error code number) should be stored as a separate attribute in a subclass. The ``raise`` statement will be changed to require that any object passed to it must inherit from BaseException. This will make sure that all exceptions fall within a single hierarchy that is anchored at BaseException [#hierarchy-good]_. This also guarantees a basic interface that is inherited from BaseException. The change to ``raise`` will be enforced starting in Python 3.0 (see the `Transition Plan`_ below). With BaseException being the root of the exception hierarchy, Exception will now inherit from it. Exception Hierarchy Changes =========================== With the exception hierarchy now even more important since it has a basic root, a change to the existing hierarchy is called for. As it stands now, if one wants to catch all exceptions that signal an error *and* do not mean the interpreter should be allowed to exit, you must specify all but two exceptions specifically in an ``except`` clause or catch the two exceptions separately and then re-raise them and have all other exceptions fall through to a bare ``except`` clause:: except (KeyboardInterrupt, SystemExit): raise except: ... That is needlessly explicit. This PEP proposes moving KeyboardInterrupt and SystemExit to inherit directly from BaseException. :: - BaseException |- KeyboardInterrupt |- SystemExit |- Exception |- (all other current built-in exceptions) Doing this makes catching Exception more reasonable. It would catch only exceptions that signify errors. Exceptions that signal that the interpreter should exit will not be caught and thus be allowed to propagate up and allow the interpreter to terminate. KeyboardInterrupt has been moved since users typically expect an application to exit when the press the interrupt key (usually Ctrl-C). If people have overly broad ``except`` clauses the expected behaviour does not occur. SystemExit has been moved for similar reasons. Since the exception is raised when ``sys.exit()`` is called the interpreter should normally be allowed to terminate. Unfortunately overly broad ``except`` clauses can prevent the explicitly requested exit from occurring. To make sure that people catch Exception most of the time, various parts of the documentation and tutorials will need to be updated to strongly suggest that Exception be what programmers want to use. Bare ``except`` clauses or catching BaseException directly should be discouraged based on the fact that KeyboardInterrupt and SystemExit almost always should be allowed to propagate up. Transition Plan =============== Since semantic changes to Python are being proposed, a transition plan is needed. The goal is to end up with the new semantics being used in Python 3.0 while providing a smooth transition for 2.x code. All deprecations mentioned in the plan will lead to the removal of the semantics starting in the version following the initial deprecation. Here is BaseException as implemented in the 2.x series:: class BaseException(object): """Superclass representing the base of the exception hierarchy. The __getitem__ method is provided for backwards-compatibility and will be deprecated at some point. """ def __init__(self, *args): """Set the 'args' attribute.""" self.args = args def __str__(self): """Return the str of args[0] or args, depending on length.""" return str(self.args[0] if len(self.args) <= 1 else self.args) def __repr__(self): func_args = repr(self.args) if self.args else "()" return self.__class__.__name__ + func_args def __getitem__(self, index): """Index into arguments passed in during instantiation. Provided for backwards-compatibility and will be deprecated. """ return self.args[index] Deprecation of features in Python 2.9 is optional. This is because it is not known at this time if Python 2.9 (which is slated to be the last version in the 2.x series) will actively deprecate features that will not be in 3.0 . It is conceivable that no deprecation warnings will be used in 2.9 since there could be such a difference between 2.9 and 3.0 that it would make 2.9 too "noisy" in terms of warnings. Thus the proposed deprecation warnings for Python 2.9 will be revisited when development of that version begins to determine if they are still desired. * Python 2.5 [done] - all standard exceptions become new-style classes - introduce BaseException - Exception, KeyboardInterrupt, and SystemExit inherit from BaseException - deprecate raising string exceptions * Python 2.6 - deprecate catching string exceptions - deprecate ``message`` attribute (see `Retracted Ideas`_) * Python 2.7 - deprecate raising exceptions that do not inherit from BaseException - remove ``message`` attribute * Python 2.8 - deprecate catching exceptions that do not inherit from BaseException * Python 2.9 - deprecate ``__getitem__`` (optional) * Python 3.0 [done] - drop everything that was deprecated above: + string exceptions (both raising and catching) + all exceptions must inherit from BaseException + drop ``__getitem__`` Retracted Ideas =============== A previous version of this PEP that was implemented in Python 2.5 included a 'message' attribute on BaseException. Its purpose was to begin a transition to BaseException accepting only a single argument. This was to tighten the interface and to force people to use attributes in subclasses to carry arbitrary information with an exception instead of cramming it all into ``args``. Unfortunately, while implementing the removal of the ``args`` attribute in Python 3.0 at the PyCon 2007 sprint [#pycon2007-sprint-email]_, it was discovered that the transition was very painful, especially for C extension modules. It was decided that it would be better to deprecate the ``message`` attribute in Python 2.6 (and remove in Python 2.7 and Python 3.0) and consider a more long-term transition strategy in Python 3.0 to remove multiple-argument support in BaseException in preference of accepting only a single argument. Thus the introduction of ``message`` and the original deprecation of ``args`` has been retracted. References ========== .. [#pep348] PEP 348 (Exception Reorganization for Python 3.0) http://www.python.org/peps/pep-0348.html .. [#hierarchy-good] python-dev Summary for 2004-08-01 through 2004-08-15 http://www.python.org/dev/summary/2004-08-01_2004-08-15.html#an-exception-i… .. [#SF_1104669] SF patch #1104669 (new-style exceptions) http://www.python.org/sf/1104669 .. [#pycon2007-sprint-email] python-3000 email ("How far to go with cleaning up exceptions") http://mail.python.org/pipermail/python-3000/2007-March/005911.html Copyright ========= This document has been placed in the public domain. .. Local Variables: mode: indented-text indent-tabs-mode: nil sentence-end-double-space: t fill-column: 70 End:

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Re: [Python-Dev] [Distutils] unicode bug in distutils
by Phillip J. Eby April 5, 2009

April 5, 2009

At 02:47 PM 2/24/2007 -0600, Tarek Ziadé wrote: >I have created a setup.py file for distirbution and I bumped into >a small bug when i tried to set my name in the contact field (Tarek Ziadé) > >Using string (utf8 file): > >setup( > maintainer="Tarek Ziadé" >) > >leads to: > > File ".../lib/python2.5/distutils/command/register.py", line 162, in > send_metadata > auth) > File ".../lib/python2.5/distutils/command/register.py", line 257, in > post_to_server > value = unicode(value).encode("utf-8") >UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 10: >ordinal not in range(128) > > >Using unicode: > >setup( > maintainer=u"Tarek Ziadé" >) > >leads to: > > File ".../lib/python2.5/distutils/dist.py", line 1094, in write_pkg_file > file.write('Author: %s\n' % self.get_contact() ) >UnicodeEncodeError: 'ascii' codec can't encode character u'\xe9' in >position 18: ordinal not in range(128) > >I would propose a patch for this problem but i don't know what would be >the best input (i guess unicode > for names) At 05:45 PM 2/24/2007 -0500, Tres Seaver wrote: >Don't you still need to tell Python about the encoding of your string >literals [1] [2] ? E.g.:: That's not the problem, it's that the code that writes the PKG-INFO file doesn't handle Unicode. See distutils.dist.DistributionMetadata.write_pkg_info(). It needs to use a file with encoding support, if it's doing unicode However, there's currently no standard, as far as I know, for what encoding the PKG-INFO file should use. Meanwhile, the 'register' command accepts Unicode, but is broken in handling it. Essentially, the problem is that Python 2.5 broke this by adding a unicode *requirement* to the "register" command. Previously, register simply sent whatever you gave it, and the PKG-INFO writing code still does. Unfortunately, this means that there is no longer any one value that you can use for your name that will be accepted by both "register" and anything that writes a PKG-INFO file. Both register and write_pkg_info() are arguably broken here, and should be able to work with either strings or unicode, and degrade gracefully in the event of non-ASCII characters in a string. (Because even though "register" is only run by the package's author, users may run other commands that require a PKG-INFO, so a package prepared using Python <2.5 must still be usable with Python 2.5 distutils, and Python <2.5 allows 8-bit maintainer names.) Unfortunately, this isn't fixable until there's a new 2.5.x release. For previous Python versions, both register and write_pkg_info() accepted 8-bit strings and passed them on as-is, so the only workaround for this issue at the moment is to revert to Python 2.4 or less.

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Python + Java Integration
by Chas Emerick Dec. 5, 2008

Dec. 5, 2008

This may seem like it's coming out of left field for a minute, but bear with me. There is no doubt that Ruby's success is a concern for anyone who sees it as diminishing Python's status. One of the reasons for Ruby's success is certainly the notion (originally advocated by Bruce Tate, if I'm not mistaken) that it is the "next Java" -- the language and environment that mainstream Java developers are, or will, look to as a natural next step. One thing that would help Python in this "debate" (or, perhaps simply put it in the running, at least as a "next Java" candidate) would be if Python had an easier migration path for Java developers that currently rely upon various third-party libraries. The wealth of third-party libraries available for Java has always been one of its great strengths. Ergo, if Python had an easy-to-use, recommended way to use those libraries within the Python environment, that would be a significant advantage to present to Java developers and those who would choose Ruby over Java. Platform compatibility is always a huge motivator for those looking to migrate or upgrade. In that vein, I would point to JPype (http://jpype.sourceforge.net). JPype is a module that gives "python programs full access to java class libraries". My suggestion would be to either: (a) include JPype in the standard library, or barring that, (b) make a very strong push to support JPype (a) might be difficult or cumbersome technically, as JPype does need to build against Java headers, which may or may not be possible given the way that Python is distributed, etc. However, (b) is very feasible. I can't really say what "supporting JPype" means exactly -- maybe GvR and/or other heavyweights in the Python community make public statements regarding its existence and functionality, maybe JPype gets a strong mention or placement on python.org....all those details are obviously not up to me, and I don't know the workings of the "official" Python organizations enough to make serious suggestions. Regardless of the form of support, I think raising people's awareness of JPype and what it adds to the Python environment would be a Good Thing (tm). For our part, we've used JPype to make PDFTextStream (our previously Java-only PDF text extraction library) available and supported for Python. You can read some about it here: http://snowtide.com/PDFTextStream.Python And I've blogged about how PDFTextStream.Python came about, and how we worked with Steve Ménard, the maintainer of JPype, to make it all happen (watch out for this URL wrapping): http://blog.snowtide.com/2006/08/21/working-together-pythonjava-open- sourcecommercial Cheers, Chas Emerick Founder, Snowtide Informatics Systems Enterprise-class PDF content extraction cemerick(a)snowtide.com http://snowtide.com | +1 413.519.6365

3 2

I would like an Python account
by Victor Stinner Oct. 6, 2008

Oct. 6, 2008

Hi, Would it possible to get more permissions on Python bugtracker, especially to add keywords, close a duplicate bug, etc.? I also would like an SVN account for Python trunk and Python 3000 branch. I know that both branches are near "frozen" and commit are only allowed after patch review and/or discussion (on the mailing list or the bug tracker. So I will after the final versions (2.6 and 3.0) to commit. Or would it be possible to have a "mentor"? Someone to ask questions about Python SVN/bug tracker, or someone who reviews my patchs/commits. -- Victor Stinner aka haypo http://www.haypocalc.com/blog/

3 4

Re: [Python-Dev] [Python-3000] New proposition for Python3 bytes filename issue
by Victor Stinner Oct. 1, 2008

Oct. 1, 2008

Le Monday 29 September 2008 18:45:28 Georg Brandl, vous avez écrit : > If I had to choose, I'd still argue for the modified UTF-8 as filesystem > encoding (if it were UTF-8 otherwise), despite possible surprises when a > such-encoded filename escapes from Python. If I understand correctly this solution. The idea is to change the default file system encoding, right? Eg. if your filesystem is UTF-8, use ISO-8859-1 to make sure that UTF-8 conversion will never fail. Let's try with an ugly directory on my UTF-8 file system: $ find . ./têste ./ô ./a?b ./dossié ./dossié/abc ./dir?name ./dir?name/xyz Python3 using encoding=ISO-8859-1: >>> import os; os.listdir(b'.') [b't\xc3\xaaste', b'\xc3\xb4', b'a\xffb', b'dossi\xc3\xa9', b'dir\xffname'] >>> files=os.listdir('.'); files ['tÃªste', 'Ã´', 'aÿb', 'dossiÃ©', 'dirÿname'] >>> open(files[0]).close() >>> os.listdir(files[-1]) ['xyz'] Ok, I have unicode filenames and I'm able to open a file and list a directory. The problem is now to display correctly the filenames. For me "unicode" sounds like "text (characters) encoded in the correct charset". In this case, unicode is just a storage for *bytes* in a custom charset. How can we mix <custom unicode (bytes encoded in ISO-8859-1)> with <real unicode>? Eg. os.path.join('dossiÃ©', "fichié") : first argument is encoded in ISO-8859-1 whereas the second argument is encoding in Unicode. It's something like that: str(b'dossi\xc3\xa9', 'ISO-8859-1') + '/' + 'fichi\xe9' Whereas the correct (unicode) result should be: 'dossié/fichié' as bytes in ISO-8859-1: b'dossi\xc3\xa9/fichi\xc3\xa9' as bytes in UTF-8: b'dossi\xe9/fichi\xe9' Change the default file system encoding to store bytes in Unicode is like introducing a new Python type: <fake Unicode for filename hacks>. -- Victor Stinner aka haypo http://www.haypocalc.com/blog/

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Python security team
by Victor Stinner Oct. 1, 2008

Oct. 1, 2008

Hi, I would like to know if a Python security team does exist. I sent an email about an imageop issue, and I didn't get any answer. Later I learned that a security ticket was created, I don't have access to it. First, I would like to access to these informations. Not only this issue, but all security related issues. I have some knowledges about security and I can help to resolve issues and/or estimate the criticity of an issue. Second, I would like to help to fix all Python security issues. It looks like Python community isn't very reactive (proactive?) about security. Eg. a DoS was reported in smtpd server (integrated to Python)... 15 months ago. A patch is available but it's not applied in Python trunk. Third, I'm also looking for a document explaining "how Python is secure" (!). If an user can run arbitrary Python code, we know that it can do anything (read/remove any file, create/kill any process, read/write anywhere in memory, etc.). Brett wrote a paper about CPython sandboxing. PyPy is also working on sandboxing using two interpreters: one has high priviledge and execute instructions from the second interpreter (after checking the permissions and arguments). So is there somewhere a document to explain to current status of Python security? -- Victor Stinner aka haypo http://www.haypocalc.com/blog/

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Re: [Python-Dev] Patch for an initial support of bytes filename in Python3
by glyph＠divmod.com Oct. 1, 2008

Oct. 1, 2008

On 12:47 am, victor.stinner(a)haypocalc.com wrote: This is the most sane contribution I've seen so far :). >See attached patch: python3_bytes_filename.patch > >Using the patch, you will get: >- open() support bytes >- listdir(unicode) -> only unicode, *skip* invalid filenames > (as asked by Guido) Forgive me for being a bit dense, but I couldn't find this hunk in the patch. Do I understand properly that (listdir(bytes) -> bytes)? If so, this seems basically sane to me, since it provides text behavior where possible and allows more sophisticated filesystem wrappers (i.e. Twisted's FilePath, Will McGugan's "FS") to do more tricky things, separating filenames for display to the user and filenames for exchange with the FS. >- remove os.getcwdu() >- create os.getcwdb() -> bytes >- glob.glob() support bytes >- fnmatch.filter() support bytes >- posixpath.join() and posixpath.split() support bytes It sounds like maybe there should be some 2to3 fixers in here somewhere, too? Not necessarily as part of this patch, but somewhere related? I don't know what they would do, but it does seem quite likely that code which was previously correct under 2.6 (using bytes) would suddenly be mixing bytes and unicode with these APIs.

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Re: [Python-Dev] [Python-3000] New proposition for Python3 bytes filename issue
by "Martin v. Löwis" Oct. 1, 2008

Oct. 1, 2008

>> On Windows, we might reject bytes filenames for all file operations: open(), >> unlink(), os.path.join(), etc. (raise a TypeError or UnicodeError) > > Since I've seen no objections to this yet: please no. If we offer a > "lower-level" bytes filename API, it should work for all platforms. Unfortunately, it can't. You cannot represent all possible file names in a byte string in Windows (just as you can't do so in a Unicode string on Unix). So using byte strings on Windows would work for some files, but fail for others. In particular, listdir might give you a list of file names which you then can't open/stat/recurse into. (of course, you could use UTF-8 as the file system encoding on Windows, but then you will have to rewrite a lot of C code first) Regards, Martin

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Re: [Python-Dev] [Python-3000] New proposition for Python3 bytes filename issue
by Guido van Rossum Oct. 1, 2008

Oct. 1, 2008

On Tue, Sep 30, 2008 at 12:42 PM, Terry Reedy <tjreedy(a)udel.edu> wrote: > Guido van Rossum wrote: >> >> On Tue, Sep 30, 2008 at 11:13 AM, Georg Brandl <g.brandl(a)gmx.net> wrote: >>> >>> Victor Stinner schrieb: >>>> >>>> On Windows, we might reject bytes filenames for all file operations: >>>> open(), >>>> unlink(), os.path.join(), etc. (raise a TypeError or UnicodeError) >>> >>> Since I've seen no objections to this yet: please no. If we offer a >>> "lower-level" bytes filename API, it should work for all platforms. >> >> I'm not sure either way. I've heard it claim that Windows filesystem >> APIs use Unicode natively. Does Python 3.0 on Windows currently >> support filenames expressed as bytes? Are they encoded first before >> passing to the Unicode APIs? Using what encoding? > > In 3.0rc1, the listdir doc needs updating: > "os.listdir(path) > Return a list containing the names of the entries in the directory. The list > is in arbitrary order. It does not include the special entries '.' and '..' > even if they are present in the directory. Availability: Unix, Windows. > > On Windows NT/2k/XP and Unix, if path is a Unicode object, the result will > be a list of Unicode objects." > > s/Unicode/bytes/ at least for Windows. > >>>> os.listdir(b'.') > [b'countries.txt', b'multeetest.py', b't1.py', b't1.pyc', b't2.py', b'tem', > b'temp.py', b'temp.pyc', b'temp2.py', b'temp3.py', b'temp4.py', b'test.py', > b'z', b'z.txt'] > > The bytes names do not work however: > >>>> t=open(b'tem') > Traceback (most recent call last): > File "<pyshell#23>", line 1, in <module> > t=open(b'tem') > File "C:\Programs\Python30\lib\io.py", line 284, in __new__ > return open(*args, **kwargs) > File "C:\Programs\Python30\lib\io.py", line 184, in open > raise TypeError("invalid file: %r" % file) > TypeError: invalid file: b'tem' > > Is this what you were asking? No, that's because bytes is missing from the explicit list of allowable types in io.open. Victor has a one-line trivial patch for this. Could you try this though? >>> import _fileio >>> _fileio._FileIO(b'tem') -- --Guido van Rossum (home page: http://www.python.org/~guido/)

2 1

Filename as byte string in python 2.6 or 3.0?
by Victor Stinner Oct. 1, 2008

Oct. 1, 2008

Hi, I read that Python 2.6 is planned to Wednesday. One bug is is still open and important for me: Python 2.6/3.0 are unable to use filename as byte strings. http://bugs.python.org/issue3187 The problem =========== On Windows, all filenames are unicode strings (I guess UTF-16-LE), but on UNIX for historical reasons, filenames are byte strings. On Linux, you can expect UTF-8 valid filenames but sometimes (eg. copy from a FAT32 USB key to an ext3 filesystem) you get invalid filename (byte string in a different charset than your default filesystem encoding (utf8)). Python functions using filenames ================================ In Python, you have (incomplete list): - filename producer: os.listdir(), os.walk(), glob.glob() - filename manipulation: os.path.*() - access file: open(), os.unlink(), shutil.rmtree() If you give unicode to producer, they return unicode _or_ byte strings (type may change for each filename :-/). Guido proposed to break this behaviour: raise an exception if unicode conversion fails. We may consider an option like "skip invalid". If you give bytes to producer, they only return byte strings. Great. Filename manipulation: in python 2.6/3.0, os.path.*() is not compatible with the type "bytes". So you can not use os.path.join(<your unicode path>, <bytes filename>) *nor* os.path.join(<your bytes path>, <bytes filename>) because os.path.join() (eg. with the posix version) uses path.endswith('/'). Access file: open() rejects the type bytes (it's just a test, open() supports bytes if you remove the test). As I remember, unlink() is compatible with bytes. But rmtree() fails because it uses os.path.join() (even if you give bytes directory, join() fails). Solutions ========= - producer: unicode => *only* unicode // bytes => bytes - manipulation: support both unicode and bytes but avoid (when it's possible) to mix bytes and characters - open(): allow bytes I implemented these solutions as a patch set attached to the issue #3187: * posix_path_bytes.patch: fix posixpath.join() to support bytes * io_byte_filename.patch: open() allows bytes filename * fnmatch_bytes.patch: patch fnmatch.filter() to accept bytes filenames * glob1_bytes.patch: fix glob.glob() to accept invalid directory name Mmmh, there is no patch for stop os.listdir() on invalid filename. Priority ======== I think that the problem is important because it's a regression from 2.5 to 2.6/3.0. Python 2.5 uses bytes filename, so it was possible to open/unlink "invalid" unicode strings (since it's not unicode but bytes). Well, if it's too late for the final versions, this problem should be at least fixed quickly. Test the problem ================ Example to create invalid filenames on Linux: $ mkdir /tmp/test $ cd /tmp/test $ touch $(echo -e "a\xffb") $ mkdir $(echo -e "dir\xffname") $ touch $(echo -e "dir\xffname/file") $ find . ./a?b ./dir?name ./dir?name/file Python 2.5: >>> import os >>> os.listdir('.') ['a\xffb', 'dir\xffname'] >>> open(os.listdir('.')[0]).close() # open file: ok >>> os.unlink(os.listdir('.')[0]) # remove file: ok >>> os.listdir('.') ['dir\xffname'] >>> shutil.rmtree(os.listdir('.')[0]) # remove dir: ok Wrong solutions =============== New type -------- I proposed an ugly type "InvalidFilename" mixing bytes and characters. As everybody using unicode knows, it's a bad idea :-) (and it introduces a new type). Convert bytes to unicode (replace) ---------------------------------- unicode_filename = unicode(bytes_filename, charset, "replace") Ok, you will get valid unicode strings which can be used in os.path.join() & friends, but open() or unlink() will fails because this filename doesn't exist! -- Victor Stinner aka haypo http://www.haypocalc.com/blog/

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Re: [Python-Dev] [Python-3000] New proposition for Python3 bytes filename issue
by "Martin v. Löwis" Sept. 30, 2008

Sept. 30, 2008

> Oh, ok. I had assumed Windows just uses a fixed encoding without the problem > of misencoded filenames. It's the other way 'round: On Windows, Unicode file names are the natural choice, and byte strings have limitations. In a sense, Windows got it right - but then, they started later. Unix missed the opportunity of declaring that all file APIs are UTF-8 (except for Plan-9 and OS X, neither being "true" Unix). Regards, Martin

2 3

Re: [Python-Dev] [Python-3000] New proposition for Python3 bytes filename issue
by Guido van Rossum Sept. 30, 2008

Sept. 30, 2008

On Mon, Sep 29, 2008 at 11:22 PM, Georg Brandl <g.brandl(a)gmx.net> wrote: > No, that was not what I meant (although it is another possibility). As I wrote, > Martin's proposal that I support here is using the modified UTF-8 codec that > successfully roundtrips otherwise invalid UTF-8 data. I thought that the "successful rountripping" pretty much stopped as soon as the unicode data is exported to somewhere else -- doesn't it contain invalid surrogate sequences? In general, I'm very reluctant to use utf-8b given that it doesn't seem to be well documented as a standard anywhere. Providing some minimal APIs that can process raw-bytes filenames still makes more sense -- it is mostly analogous of our treatment of text files, where the underlying binary data is also accessible. > You seem to forget that (disregarding OSX here, since it already enforces > UTF-8) the majority of file names on Posix systems will be encoded correctly. Apparently under certain circumstances (external FS mounted) OSX can also have non-UTF-8 filenames. [...] > With the filenames decoded by UTF-8, your files named têste, ô, dossié will > be displayed and handled correctly. The others are *invalid* in the filesystem > encoding UTF-8 and therefore would be represented by something like > > u'dir\uXXffname' where XX is some private use Unicode namespace. It won't look > pretty when printed, but then, what do other applications do? They e.g. display > a question mark as you show above, which is not better in terms of readability. > > But it will work when given to a filename-handling function. Valid filenames > can be compared to Unicode strings. > > A real-world example: OpenOffice can't open files with invalid bytes in their > name. They are displayed in the "Open file" dialog, but trying to open fails. > This regularly drives me crazy. Let's not make Python not work this way too, > or, even worse, not even display those filenames. How can it *regularly* drive you crazy when "the majority of fie names [...] encoded correctly" (as you assert above)? -- --Guido van Rossum (home page: http://www.python.org/~guido/)

4 8

Re: [Python-Dev] [Python-3000] New proposition for Python3 bytes filename issue
by Marcin 'Qrczak' Kowalczyk Sept. 30, 2008

Sept. 30, 2008

2008/9/30 Glenn Linderman <v+python(a)g.nevcal.com>: > So the problem is that a Unicode file system interface can't deal with > non-UTF-8 byte streams as file names. > > So it seems there are four suggested approaches, all of which have aspects > that are inconvenient. Let's not forget what happens when a non-UTF-8 file name is read from a file or written to a file, under the assumption that the filename is written to the file directly (which probably breaks for filenames containing newlines or such). > 4) Use of bytes APIs on FS interfaces. This seems to be the "solution" > adopted by Posix that creates the "problem" encountered by Unicode-native > applications. It is cumbersome to deal with within applications that > attempt to display the names. What do Posix-style "open file" dialog boxes > do in this case? http://library.gnome.org/devel/glib/stable/glib-Character-Set-Conversion.ht… I used to observe three different ways to display such filenames within gedit (including %xx and \xx escapes), but now it is consistent, probably because it switched to using the above function everywhere: $ touch $'abc\xffz' $ gedit The Open dialog shows: abc�z (invalid encoding) When the file is open, the window title and the tab title show: abc�z and the same is in recent file list. It has a bug: it appends " (invalid encoding)" even if the filename contains a correctly encoded U+FFFD character. Nautilus has the same behavior and the same bug because this is a design bug of that function which does not allow to tell whether the conversion was successful. A filename containing a newline is sometimes displayed in two lines, and sometimes with a U+000A character from a fallback font (hex character number in a box). -- Marcin Kowalczyk qrczak(a)knm.org.pl http://qrnik.knm.org.pl/~qrczak/

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Re: [Python-Dev] [Python-3000] New proposition for Python3 bytes filename issue
by Guido van Rossum Sept. 30, 2008

Sept. 30, 2008

On Tue, Sep 30, 2008 at 1:12 PM, Terry Reedy <tjreedy(a)udel.edu> wrote: > Terry Reedy wrote: >> >> Guido van Rossum wrote: > >>> I'm not sure either way. I've heard it claim that Windows filesystem >>> APIs use Unicode natively. Does Python 3.0 on Windows currently >>> support filenames expressed as bytes? Are they encoded first before >>> passing to the Unicode APIs? Using what encoding? > >> [os.listdir(bytes) returns list of bytes, open(bytes) fails] > > More: > > The path functions seem also do not work: > >>>> op.abspath(b'tem') > ... > path = path.replace("/", "\\") > TypeError: expected an object with the buffer interface > > The error message is a bit cryptic given that the problem is that the > arguments to replace should be bytes instead of strings for a bytes path. > > .basename fails with > ... > while i and p[i-1] not in '/\\': > TypeError: 'in <string>' requires string as left operand, not int > > os.rename, os.stat, os.mkdir, os.rmdir work. I presume same is true for > others that normally work on windows. It looks roughly like the system calls do support bytes (using what encoding?) but the Python code in os.path doesn't. This is the same as the status quo on Linux. -- --Guido van Rossum (home page: http://www.python.org/~guido/)

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Re: [Python-Dev] [Python-3000] New proposition for Python3 bytes filename issue
by Guido van Rossum Sept. 30, 2008

Sept. 30, 2008

On Tue, Sep 30, 2008 at 11:13 AM, Georg Brandl <g.brandl(a)gmx.net> wrote: > Victor Stinner schrieb: >> On Windows, we might reject bytes filenames for all file operations: open(), >> unlink(), os.path.join(), etc. (raise a TypeError or UnicodeError) > > Since I've seen no objections to this yet: please no. If we offer a > "lower-level" bytes filename API, it should work for all platforms. I'm not sure either way. I've heard it claim that Windows filesystem APIs use Unicode natively. Does Python 3.0 on Windows currently support filenames expressed as bytes? Are they encoded first before passing to the Unicode APIs? Using what encoding? -- --Guido van Rossum (home page: http://www.python.org/~guido/)

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Re: [Python-Dev] Patch for an initial support of bytes filename in Python3
by Bill Janssen Sept. 30, 2008

Sept. 30, 2008

Victor Stinner <victor.stinner(a)haypocalc.com> wrote: > - listdir(unicode) -> only unicode, *skip* invalid filenames > (as asked by Guido) Is there an option listdir(bytes) which will return *all* filenames (as byte sequences)? Otherwise, this seems troubling to me; *something* should be returned for filenames which can't be represented, even if it's only None. Bill

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Re: [Python-Dev] [Python-3000] New proposition for Python3 bytes filename issue
by Guido van Rossum Sept. 30, 2008

Sept. 30, 2008

> Victor Stinner schrieb: (Thanks Victor for moving this to the list. Having a discussion in the tracker is really painful, I find.) >> POSIX OS >> -------- >> >> The default behaviour should be to use unicode and raise an error if >> conversion to unicode fails. It should also be possible to use bytes using >> bytes arguments and optional arguments (for getcwd). >> >> - listdir(unicode) -> unicode and raise an error on invalid filename I know I keep flipflopping on this one, but the more I think about it the more I believe it is better to drop those names than to raise an exception. Otherwise a "naive" program that happens to use os.listdir() can be rendered completely useless by a single non-UTF-8 filename. Consider the use of os.listdir() by the glob module. If I am globbing for *.py, why should the presence of a file named b'\xff' cause it to fail? Robust programs using os.listdir() should use the bytes->bytes version. >> - listdir(bytes) -> bytes >> - getcwd() -> unicode >> - getcwd(bytes=True) -> bytes >> - open(): accept bytes or unicode >> >> os.path.*() should accept operations on bytes filenames, but maybe not on >> bytes+unicode arguments. os.path.join('directory', b'filename'): raise an >> error (or use *implicit* conversion to bytes)? (Yeah, it should be all bytes or all strings.) On Mon, Sep 29, 2008 at 9:45 AM, Georg Brandl <g.brandl(a)gmx.net> wrote: > This approach (changing all path-handling functions to accept either bytes > or string, but not both) is doomed in my eyes. First, there are lots of them, > second, they are not only in os.path but in many modules and also in user > code, and third, I see no clean way of implementing them in the specified way. > (Just try to do it with os.path.join as an example; I couldn't find the > good way to write it, only the bad and the ugly...) It doesn't have to be supported for all operations -- just enough to be able to access all the system calls. and do the most basic pathname manipulations (split and join -- almost everything else can be built out of those). > If I had to choose, I'd still argue for the modified UTF-8 as filesystem > encoding (if it were UTF-8 otherwise), despite possible surprises when a > such-encoded filename escapes from Python. I'm having a hard time finding info about UTF-8b. Does anyone have a decent link? I noticed that OSX has a different approach yet. I believe it insists on valid UTF-8 filenames. It may even require some normalization but I don't know if the kernel enforces this. I tried to create a file named b'\xff' and it came out as %ff. Then "rm %ff" worked. So I think it may be replacing all bad UTF8 sequences with their % encoding. The "set filesystem encoding to be Latin-1" approach has a certain charm as well, but clearly would be a mistake on OSX, and probably on other systems too (whenever the user doesn't think in Latin-1). -- --Guido van Rossum (home page: http://www.python.org/~guido/)

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when is path==NULL?
by Ulrich Eckhardt Sept. 30, 2008

Sept. 30, 2008

Hi! I'm looking at trunk/Python/sysmodule.c, function PySys_SetArgv(). In that function, there is code like this: PyObject* path = PySys_GetObject("path"); ... if (path != NULL) { ... } My intuition says that if path==NULL, something is very wrong. At least I would expect to get 'None', but never NULL, except when out of memory. So, for the case that path==NULL', I would simply invoke Py_FatalError("no mem for sys.path"), similarly to the other call there. Sounds reasonable? Uli -- Sator Laser GmbH Geschäftsführer: Thorsten Föcking, Amtsgericht Hamburg HR B62 932 ************************************************************************************** Visit our website at <http://www.satorlaser.de/> ************************************************************************************** Diese E-Mail einschließlich sämtlicher Anhänge ist nur für den Adressaten bestimmt und kann vertrauliche Informationen enthalten. Bitte benachrichtigen Sie den Absender umgehend, falls Sie nicht der beabsichtigte Empfänger sein sollten. Die E-Mail ist in diesem Fall zu löschen und darf weder gelesen, weitergeleitet, veröffentlicht oder anderweitig benutzt werden. E-Mails können durch Dritte gelesen werden und Viren sowie nichtautorisierte Änderungen enthalten. Sator Laser GmbH ist für diese Folgen nicht verantwortlich. **************************************************************************************

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Re: [Python-Dev] [Python-3000] New proposition for Python3 bytes filename issue
by Adam Olsen Sept. 30, 2008

Sept. 30, 2008

On Tue, Sep 30, 2008 at 12:22 AM, Georg Brandl <g.brandl(a)gmx.net> wrote: > Victor Stinner schrieb: >> Le Monday 29 September 2008 18:45:28 Georg Brandl, vous avez écrit : >>> If I had to choose, I'd still argue for the modified UTF-8 as filesystem >>> encoding (if it were UTF-8 otherwise), despite possible surprises when a >>> such-encoded filename escapes from Python. >> >> If I understand correctly this solution. The idea is to change the default >> file system encoding, right? Eg. if your filesystem is UTF-8, use ISO-8859-1 >> to make sure that UTF-8 conversion will never fail. > > No, that was not what I meant (although it is another possibility). As I wrote, > Martin's proposal that I support here is using the modified UTF-8 codec that > successfully roundtrips otherwise invalid UTF-8 data. > > You seem to forget that (disregarding OSX here, since it already enforces > UTF-8) the majority of file names on Posix systems will be encoded correctly. > >> Let's try with an ugly directory on my UTF-8 file system: >> $ find >> .. >> ../têste >> ../ô >> ../a?b >> ../dossié >> ../dossié/abc >> ../dir?name >> ../dir?name/xyz >> >> Python3 using encoding=ISO-8859-1: >>>>> import os; os.listdir(b'.') >> [b't\xc3\xaaste', b'\xc3\xb4', b'a\xffb', b'dossi\xc3\xa9', b'dir\xffname'] >>>>> files=os.listdir('.'); files >> ['tÃªste', 'Ã´', 'aÿb', 'dossiÃ(c)', 'dirÿname'] >>>>> open(files[0]).close() >>>>> os.listdir(files[-1]) >> ['xyz'] >> >> Ok, I have unicode filenames and I'm able to open a file and list a directory. >> The problem is now to display correctly the filenames. >> >> For me "unicode" sounds like "text (characters) encoded in the correct >> charset". In this case, unicode is just a storage for *bytes* in a custom >> charset. > >> How can we mix <custom unicode (bytes encoded in ISO-8859-1)> with <real >> unicode>? Eg. os.path.join('dossiÃ(c)', "fichié") : first argument is encoded >> in ISO-8859-1 whereas the second argument is encoding in Unicode. It's >> something like that: >> str(b'dossi\xc3\xa9', 'ISO-8859-1') + '/' + 'fichi\xe9' >> >> Whereas the correct (unicode) result should be: >> 'dossié/fichié' >> as bytes in ISO-8859-1: >> b'dossi\xc3\xa9/fichi\xc3\xa9' >> as bytes in UTF-8: >> b'dossi\xe9/fichi\xe9' > > With the filenames decoded by UTF-8, your files named têste, ô, dossié will > be displayed and handled correctly. The others are *invalid* in the filesystem > encoding UTF-8 and therefore would be represented by something like > > u'dir\uXXffname' where XX is some private use Unicode namespace. It won't look > pretty when printed, but then, what do other applications do? They e.g. display > a question mark as you show above, which is not better in terms of readability. > > But it will work when given to a filename-handling function. Valid filenames > can be compared to Unicode strings. > > A real-world example: OpenOffice can't open files with invalid bytes in their > name. They are displayed in the "Open file" dialog, but trying to open fails. > This regularly drives me crazy. Let's not make Python not work this way too, > or, even worse, not even display those filenames. The only way to display that file would be to transform it into some other valid unicode string. However, as that string is already valid, you've just made any files named after it impossible to open. If you extend unicode then you're unable to display that extended name[1]. I think Guido's right on this one. If I have to choose between openoffice crashing or skipping my file, I'd vastly prefer it skip it. A warning would be a nice bonus (from python or from openoffice), telling me there's a buggered file I should go fix. Renaming the file is the end solution. [1] You could argue that Unicode should add new scalars to handle all currently invalid UTF-8 sequences. They could then output to their original forms if in UTF-8, or a mundane form in UTF-16 and UTF-32. However, I suspect "we don't want to add validation to linux" will not be a very persuasive argument. -- Adam Olsen, aka Rhamphoryncus

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Status of MS Windows CE port
by Ulrich Eckhardt Sept. 30, 2008

Sept. 30, 2008

Greetings! I'm currently trying to assess the effort required for a CE port. I'm already aware of the project at http://pythonce.sourceforge.net, but I find it a waste of time to have two separate projects which then require syncing changes back and forth. Questions: - What are the feelings towards a port in the mainline? I'm aware that you are trying to get 2.6 and 3.0 out of the door and are probably not willing to risk such changes to the release code right now, but in general? - Is anyone already working on this? I know that Brad Clements made an attempt some years ago but didn't get it integrated, are there any others? Maybe even any ongoing work? - I see that you are using Subversion and Bazaar, would it be possible to get a feature branch for the CE port? I'm thinking about the effort going on at pythonce.sf.net and some further porting that I need for my specific platform. IMHO both would be better off in the same repository as your upstream sources, since merging changes back and forth is much easier that way. Thanks! Uli -- Sator Laser GmbH Geschäftsführer: Thorsten Föcking, Amtsgericht Hamburg HR B62 932 ************************************************************************************** Visit our website at <http://www.satorlaser.de/> ************************************************************************************** Diese E-Mail einschließlich sämtlicher Anhänge ist nur für den Adressaten bestimmt und kann vertrauliche Informationen enthalten. Bitte benachrichtigen Sie den Absender umgehend, falls Sie nicht der beabsichtigte Empfänger sein sollten. Die E-Mail ist in diesem Fall zu löschen und darf weder gelesen, weitergeleitet, veröffentlicht oder anderweitig benutzt werden. E-Mails können durch Dritte gelesen werden und Viren sowie nichtautorisierte Änderungen enthalten. Sator Laser GmbH ist für diese Folgen nicht verantwortlich. **************************************************************************************

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Re: [Python-Dev] Patch for an initial support of bytes filename in Python3
by Brett Cannon Sept. 30, 2008

Sept. 30, 2008

On Mon, Sep 29, 2008 at 5:47 PM, Victor Stinner <victor.stinner(a)haypocalc.com> wrote: > Hi, > > See attached patch: python3_bytes_filename.patch > Patches should go on the tracker, not the mailing list. Otherwise it will just get lost. -Brett

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Re: [Python-Dev] Real segmentation fault handler
by Ralf W. Grosse-Kunstleve Sept. 30, 2008

Sept. 30, 2008

FWIW: I didn't have much luck translating segfaults into exceptions. It (seemed) to work on some platforms, but not others; this was in the context of C++. In my experience, it is more useful to generate Python and C stack traces and bail out. I also do this for floating-point exceptions. The handlers are installed at runtime from a low-level extension module: http://cctbx.svn.sourceforge.net/viewvc/cctbx/trunk/boost_adaptbx/meta_ext.… Example output is below. It works under Linux and partially under Mac OS X. Ralf % boost_adaptbx.segmentation_fault Now dereferencing null-pointer ... show_stack(1): /net/chevy/raid1/rwgk/dist/boost_adaptbx/command_line/segmentation_fault.py(10) run show_stack(2): /net/chevy/raid1/rwgk/dist/boost_adaptbx/command_line/segmentation_fault.py(14) <module> libc backtrace (18 frames, most recent call last): /net/chevy/raid1/rwgk/bintbx_py252/base/bin/python [0x4118e9] /lib64/libc.so.6(__libc_start_main+0xf4) [0x363241e074] /net/chevy/raid1/rwgk/bintbx_py252/base/bin/python(Py_Main+0x935) [0x4123c5] /net/chevy/raid1/rwgk/bintbx_py252/base/bin/python(PyRun_SimpleFileExFlags+0x1a0) [0x4a8860] /net/chevy/raid1/rwgk/bintbx_py252/base/bin/python(PyRun_FileExFlags+0x10e) [0x4a85ce] /net/chevy/raid1/rwgk/bintbx_py252/base/bin/python(PyEval_EvalCode+0x32) [0x487402] /net/chevy/raid1/rwgk/bintbx_py252/base/bin/python(PyEval_EvalCodeEx+0x81f) [0x4873bf] /net/chevy/raid1/rwgk/bintbx_py252/base/bin/python(PyEval_EvalFrameEx+0x6bc1) [0x486541] /net/chevy/raid1/rwgk/bintbx_py252/base/bin/python(PyEval_EvalFrameEx+0x2bb9) [0x482539] /net/chevy/raid1/rwgk/bintbx_py252/base/bin/python(PyObject_Call+0x13) [0x415ae3] /net/chevy/raid1/rwgk/bintbx_py252/lib/libboost_python.so [0x2aaaaba7c6f7] /net/chevy/raid1/rwgk/bintbx_py252/lib/libboost_python.so(boost::python::handle_exception_impl(boost::function0<void>)+0x28) [0x2aaaaba87148] /net/chevy/raid1/rwgk/bintbx_py252/lib/libboost_python.so(boost::function0<void>::operator()() const+0x19e) [0x2aaaaba8816e] /net/chevy/raid1/rwgk/bintbx_py252/lib/libboost_python.so [0x2aaaaba7fef8] /net/chevy/raid1/rwgk/bintbx_py252/lib/libboost_python.so(boost::python::objects::function::call(_object*, _object*) const+0x7d) [0x2aaaaba7fb5d] /net/chevy/raid1/rwgk/bintbx_py252/lib/boost_python_meta_ext.so(boost::python::objects::caller_py_function_impl<boost::python::detail::caller<char (*)(char const*), boost::python::default_call_policies, boost::mpl::vector2<char, char const*> > >::operator()(_object*, _object*)+0x29) [0x2aaaab8470a9] /net/chevy/raid1/rwgk/bintbx_py252/lib/boost_python_meta_ext.so [0x2aaaab843790] /lib64/libc.so.6 [0x3632430f30] Segmentation fault (Python and libc call stacks above) % boost_adaptbx.divide_by_zero Now dividing by zero (in C++) ... show_stack(1): /net/chevy/raid1/rwgk/dist/boost_adaptbx/command_line/divide_by_zero.py(10) run show_stack(2): /net/chevy/raid1/rwgk/dist/boost_adaptbx/command_line/divide_by_zero.py(14) <module> libc backtrace (18 frames, most recent call last): /net/chevy/raid1/rwgk/bintbx_py252/base/bin/python [0x4118e9] /lib64/libc.so.6(__libc_start_main+0xf4) [0x363241e074] /net/chevy/raid1/rwgk/bintbx_py252/base/bin/python(Py_Main+0x935) [0x4123c5] /net/chevy/raid1/rwgk/bintbx_py252/base/bin/python(PyRun_SimpleFileExFlags+0x1a0) [0x4a8860] /net/chevy/raid1/rwgk/bintbx_py252/base/bin/python(PyRun_FileExFlags+0x10e) [0x4a85ce] /net/chevy/raid1/rwgk/bintbx_py252/base/bin/python(PyEval_EvalCode+0x32) [0x487402] /net/chevy/raid1/rwgk/bintbx_py252/base/bin/python(PyEval_EvalCodeEx+0x81f) [0x4873bf] /net/chevy/raid1/rwgk/bintbx_py252/base/bin/python(PyEval_EvalFrameEx+0x6bc1) [0x486541] /net/chevy/raid1/rwgk/bintbx_py252/base/bin/python(PyEval_EvalFrameEx+0x2bb9) [0x482539] /net/chevy/raid1/rwgk/bintbx_py252/base/bin/python(PyObject_Call+0x13) [0x415ae3] /net/chevy/raid1/rwgk/bintbx_py252/lib/libboost_python.so [0x2aaaaba7c6f7] /net/chevy/raid1/rwgk/bintbx_py252/lib/libboost_python.so(boost::python::handle_exception_impl(boost::function0<void>)+0x28) [0x2aaaaba87148] /net/chevy/raid1/rwgk/bintbx_py252/lib/libboost_python.so(boost::function0<void>::operator()() const+0x19e) [0x2aaaaba8816e] /net/chevy/raid1/rwgk/bintbx_py252/lib/libboost_python.so [0x2aaaaba7fef8] /net/chevy/raid1/rwgk/bintbx_py252/lib/libboost_python.so(boost::python::objects::function::call(_object*, _object*) const+0x7d) [0x2aaaaba7fb5d] /net/chevy/raid1/rwgk/bintbx_py252/lib/boost_python_meta_ext.so(boost::python::objects::caller_py_function_impl<boost::python::detail::caller<double (*)(double const&, double const&), boost::python::default_call_policies, boost::mpl::vector3<double, double const&, double const&> > >::operator()(_object*, _object*)+0x12a) [0x2aaaab84759a] /net/chevy/raid1/rwgk/bintbx_py252/lib/boost_python_meta_ext.so [0x2aaaab8437a4] /lib64/libc.so.6 [0x3632430f30] Floating-point error (Python and libc call stacks above) ----- Original Message ---- From: Victor Stinner <victor.stinner(a)haypocalc.com> To: python-dev(a)python.org Sent: Monday, September 29, 2008 4:05:53 PM Subject: [Python-Dev] Real segmentation fault handler Hi, I would like to be able to catch SIGSEGV in my Python code! So I started to hack Python trunk to support this feature. The idea is to use a signal handler which call longjmp(), and add setjmp() at Py_EvalFrameEx() enter. See attached ("small") patch: segfault.patch Example read.py with the *evil* ctypes module of invalid memory read: ------------------- 8< -------------- from ctypes import string_at def fault(): text = string_at(1, 10) print("text = {0!r}".format(text)) def test(): print("test: 1") try: fault() except MemoryError, err: print "ooops!" print err print("test: 2") try: fault() except MemoryError, err: print "ooops!" print err print("test: end") def main(): test() if __name__ == "__main__": main() ------------------- 8< -------------- Result: ------------------- 8< -------------- $ python read.py test: 1 sizeof()=160 ooops! segmentation fault test: 2 sizeof()=160 ooops! segmentation fault test: end ------------------- 8< -------------- Example bug1.py of a stack overflow: ---------- loop = None, for i in xrange(10**5): loop = loop, None ---------- Result: ---------- $ python -i bug1.py >>> print loop (((((((((...Traceback (most recent call last): File "<stdin>", line 1, in <module> MemoryError: segmentation fault >>> ---------- Python is able to restore a valid state (stack/heap) after a segmentation fault and raise a classical Python exception (I choosed MemoryError, but it could be a specific exception). On my computer (Ubuntu Gutsy/i386), each segfault_frame takes sizeof(sigjmpbuf) + sizeof(void*) = 160 bytes, allocated on the stack. I don't know if it's huge or not, but that will limit the number of recursive calls. The feature can be optional if we add a configure option and some #ifdef/#endif. A dedicated stack is needed to be call the signal handler on stack overflow error. I choosed 4 KB, but since I only call longjmp(), smaller stack might also works. Does other VM support such feature? JVM, Mono, .NET, etc. ? I had the idea of catching SIGSEGV after reading the issue 1069092 (stack overflow because of too many recursive calls). -- Victor Stinner aka haypo http://www.haypocalc.com/blog/

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