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>
Phillip.eby wrote:
> Author: phillip.eby
> Date: Tue Apr 18 02:59:55 2006
> New Revision: 45510
>
> Modified:
> python/trunk/Lib/pkgutil.py
> python/trunk/Lib/pydoc.py
> Log:
> Second phase of refactoring for runpy, pkgutil, pydoc, and setuptools
> to share common PEP 302 support code, as described here:
>
> http://mail.python.org/pipermail/python-dev/2006-April/063724.html
Shouldn't this new module be named "pkglib" to be in line with
the naming scheme used for all the other utility modules, e.g. httplib,
imaplib, poplib, etc. ?
> pydoc now supports PEP 302 importers, by way of utility functions in
> pkgutil, such as 'walk_packages()'. It will properly document
> modules that are in zip files, and is backward compatible to Python
> 2.3 (setuptools installs for Python <2.5 will bundle it so pydoc
> doesn't break when used with eggs.)
Are you saying that the installation of setuptools in Python 2.3
and 2.4 will then overwrite the standard pydoc included with
those versions ?
I think that's the wrong way to go if not made an explicit
option in the installation process or a separate installation
altogether.
I bothered by the fact that installing setuptools actually changes
the standard Python installation by either overriding stdlib modules
or monkey-patching them at setuptools import time.
> What has not changed is that pydoc command line options do not support
> zip paths or other importer paths, and the webserver index does not
> support sys.meta_path. Those are probably okay as limitations.
>
> Tasks remaining: write docs and Misc/NEWS for pkgutil/pydoc changes,
> and update setuptools to use pkgutil wherever possible, then add it
> to the stdlib.
Add setuptools to the stdlib ? I'm still missing the PEP for this
along with the needed discussion touching among other things,
the change of the distutils standard "python setup.py install"
to install an egg instead of a site package.
--
Marc-Andre Lemburg
eGenix.com
Professional Python Services directly from the Source (#1, Apr 18 2006)
>>> Python/Zope Consulting and Support ... http://www.egenix.com/
>>> mxODBC.Zope.Database.Adapter ... http://zope.egenix.com/
>>> mxODBC, mxDateTime, mxTextTools ... http://python.egenix.com/
________________________________________________________________________
::: Try mxODBC.Zope.DA for Windows,Linux,Solaris,FreeBSD for free ! ::::
I'm interested in how builtins could be more efficient. I've read over
some of the PEPs having to do with making global variables more
efficient (search for "global"):
http://www.python.org/doc/essays/pepparade.html
But I think the problem can be simplified by focusing strictly on
builtins.
One of my assumptions is that only a small fractions of modules override
the default builtins with something like:
import mybuiltins
__builtins__ = mybuiltins
As you probably know each access of a builtin requires two hash table
lookups. First, the builtin is not found in the list of globals. It is
then found in the list of builtins.
Why not have a means of referencing the default builtins with some sort
of index the way the LOAD_FAST op code currently works? In other words,
by default each module gets the default set of builtins indexed (where
the index indexes into an array) in a certain order. The version stored
in the pyc file would be bumped each time the set of default builtins
is changed.
I don't have very strong feelings whether things like True = (1 == 1)
would be a syntax error, but assigning to a builtin could just do the
equivalent of STORE_FAST. I also don't have very strong feelings about
whether the array of default builtins would be shared between modules.
To simulate the current behavior where attempting to assign to builtin
actually alters that module's global hashtable a separate array of
builtins could be used for each module.
As to assigning to __builtins__ (like I mentioned at the beginning of
this post) perhaps it could assign to the builtin array for those items
that have a name that matches a default builtin (such as "True" or
"len"). Those items that don't match a default builtin would just
create global variables.
Perhaps what I'm suggesting isn't feasible for reasons that have already
been discussed. But it seems like it should be possible to make "while
True" as efficient as "while 1".
--
-----------------------------------------------------------------------
| Steven Elliott | selliott4(a)austin.rr.com |
-----------------------------------------------------------------------
Should GeneratorExit inherit from Exception or BaseException?
Currently, a generator that catches Exception and continues on to yield
another value can't be closed properly (you get a runtime error pointing out
that the generator ignored GeneratorExit).
The only decent reference I could find to it in the old PEP 348/352
discussions is Guido writing [1]:
> when GeneratorExit or StopIteration
> reach the outer level of an app, it's a bug like all the others that
> bare 'except:' WANTS to catch.
(at that point in the conversation, I believe bare except was considered the
equivalent of "except Exception:")
While I agree with what Guido says about GeneratorExit being a bug if it
reaches the outer level of an app, it seems like a bit of a trap that a
correctly written generator can't write "except Exception:" without preceding
it with an "except GeneratorExit:" that reraises the exception. Isn't that
exactly the idiom we're trying to get rid of for SystemExit and KeyboardInterrupt?
Regards,
Nick.
[1] http://mail.python.org/pipermail/python-dev/2005-August/055173.html
--
Nick Coghlan | ncoghlan(a)gmail.com | Brisbane, Australia
---------------------------------------------------------------
http://www.boredomandlaziness.org
For years, Boost.Python has been doing some hacks to work around the
fact that a Windows Python distro doesn't include the debug build of
the library.
http://www.boost.org/libs/python/doc/building.html#variants
explains. We wanted to make it reasonably convenient for Windows
developers (and our distributed testers) to work with a debug build of
the Boost.Python library and of their own code. Having to download
the Python source and build the debug DLL was deemed unacceptable.
Well, those hacks have run out of road. VC++8 now detects that some
of its headers have been #included with _DEBUG and some without, and
it will refuse to build anything when it does. We have several new
hacks to work around that detection, and I think we _might_ be able to
get away with them for one more release. But it's really time to do
it right. MS is recommending that we (Boost) start distributing a
debug build of the Python DLL with Boost, but Boost really seems like
the wrong place to host such a thing. Is there any way Python.org can
make a debug build more accessible?
Thanks,
Dave
--
Dave Abrahams
Boost Consulting
www.boost-consulting.com
(Context: There's a large crowd with pitchforks and other sharp pointy
farm implements just outside the door of my office at Google. They are
making an unbelievable racket. It appears they are Google engineers
who have been bitten by a misfeature of Python, and they won't let me
go home before I have posted this message.)
The requirement that a directlry must contain an __init__.py file
before it is considered a valid package has always been controversial.
It's designed to prevent the existence of a directory with a common
name like "time" or "string" from preventing fundamental imports to
work. But the feature often trips newbie Python programmers (of which
there are a lot at Google, at our current growth rate we're probably
training more new Python programmers than any other organization
worldwide :-).
One particular egregious problem is that *subpackage* are subject to
the same rule. It so happens that there is essentially only one
top-level package in the Google code base, and it already has an
__init__.py file. But developers create new subpackages at a
frightening rate, and forgetting to do "touch __init__.py" has caused
many hours of lost work, not to mention injuries due to heads banging
against walls.
So I have a very simple proposal: keep the __init__.py requirement for
top-level pacakages, but drop it for subpackages. This should be a
small change. I'm hesitant to propose *anything* new for Python 2.5,
so I'm proposing it for 2.6; if Neal and Anthony think this would be
okay to add to 2.5, they can do so.
--
--Guido van Rossum (home page: http://www.python.org/~guido/)
see subject and http://python.org/sf/1368955
comments ?
</F>
(note sure how my previous attempt to post this ended up on
comp.lang.python instead, but I'll blame it on gmane... ;-)
PEP 333 specifies WSGI, the Python Web Server Gateway Interface v1.0;
it's written by Phillip Eby who put a lot of effort in it to make it
acceptable to very diverse web frameworks. The PEP has been well
received by web framework makers and users.
As a supplement to the PEP, Phillip has written a reference
implementation, "wsgiref". I don't know how many people have used
wsgiref; I'm using it myself for an intranet webserver and am very
happy with it. (I'm asking Phillip to post the URL for the current
source; searching for it produces multiple repositories.)
I believe that it would be a good idea to add wsgiref to the stdlib,
after some minor cleanups such as removing the extra blank lines that
Phillip puts in his code. Having standard library support will remove
the last reason web framework developers might have to resist adopting
WSGI, and the resulting standardization will help web framework users.
Last time this was brought up there were feature requests and
discussion on how "industrial strength" the webserver in wsgiref ought
to be but nothing like the flamefest that setuptools caused (no
comments please).
I'm inviting people to discuss the addition of wsgiref to the standard
library. I'd like the discussion to be finished before a3 goes out;
technically it can go in up till the b1 code freeze, but I don't
really want to push it that close. I'd like the focus of the
discussion to be "what are the risks of adding wsgiref to the stdlib";
not "what could we think of that's even better". Achieving a perfect
decision is not the goal; having general consensus that adding it
would be better than not adding is would be good. Pointing out
specific bugs in wsgiref and suggesting how they ought to be fixed is
also welcome.
--
--Guido van Rossum (home page: http://www.python.org/~guido/)
Hello,
base64 module documentation for b64decode function says, "TypeError is
raised if s were incorrectly padded or if there are non-alphabet
characters present in the string." But this doesn't seem to be the
case. Testcase:
import base64
base64.b64decode('%')
Since % is a non-alphabet character, this should raise TypeError (btw,
shouldn't this be ValueError instead?), but Python 2.4.3 silently
ignores.
I found this while experimenting with IronPython. IronPython 1.0 Beta 5 gives:
Traceback (most recent call last):
File base64, line unknown, in b64decode
SystemError: cannot decode byte: '%'
It's not TypeError, but it doesn't silently ignore either.
Seo Sanghyeon
