Python-Dev March 2010

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136 participants
91 discussions

by Guido van Rossum

I've received some enthusiastic emails from someone who wants to revive restricted mode. He started out with a bunch of patches to the CPython runtime using ctypes, which he attached to an App Engine bug: http://code.google.com/p/googleappengine/issues/detail?id=671 Based on his code (the file secure.py is all you need, included in secure.tar.gz) it seems he believes the only security leaks are __subclasses__, gi_frame and gi_code. (I have since convinced him that if we add "restricted" guards to these attributes, he doesn't need the functions added to sys.) I don't recall the exploits that Samuele once posted that caused the death of rexec.py -- does anyone recall, or have a pointer to the threads? -- --Guido van Rossum (home page: http://www.python.org/~guido/)

5 years, 9 months

PEP 3145 (With Contents)

by Eric Pruitt

Alright, I will re-submit with the contents pasted. I never use double backquotes as I think them rather ugly; that is the work of an editor or some automated program in the chain. Plus, it also messed up my line formatting and now I have lines with one word on them... Anyway, the contents of PEP 3145: PEP: 3145 Title: Asynchronous I/O For subprocess.Popen Author: (James) Eric Pruitt, Charles R. McCreary, Josiah Carlson Type: Standards Track Content-Type: text/plain Created: 04-Aug-2009 Python-Version: 3.2 Abstract: In its present form, the subprocess.Popen implementation is prone to dead-locking and blocking of the parent Python script while waiting on data from the child process. Motivation: A search for "python asynchronous subprocess" will turn up numerous accounts of people wanting to execute a child process and communicate with it from time to time reading only the data that is available instead of blocking to wait for the program to produce data [1] [2] [3]. The current behavior of the subprocess module is that when a user sends or receives data via the stdin, stderr and stdout file objects, dead locks are common and documented [4] [5]. While communicate can be used to alleviate some of the buffering issues, it will still cause the parent process to block while attempting to read data when none is available to be read from the child process. Rationale: There is a documented need for asynchronous, non-blocking functionality in subprocess.Popen [6] [7] [2] [3]. Inclusion of the code would improve the utility of the Python standard library that can be used on Unix based and Windows builds of Python. Practically every I/O object in Python has a file-like wrapper of some sort. Sockets already act as such and for strings there is StringIO. Popen can be made to act like a file by simply using the methods attached the the subprocess.Popen.stderr, stdout and stdin file-like objects. But when using the read and write methods of those options, you do not have the benefit of asynchronous I/O. In the proposed solution the wrapper wraps the asynchronous methods to mimic a file object. Reference Implementation: I have been maintaining a Google Code repository that contains all of my changes including tests and documentation [9] as well as blog detailing the problems I have come across in the development process [10]. I have been working on implementing non-blocking asynchronous I/O in the subprocess.Popen module as well as a wrapper class for subprocess.Popen that makes it so that an executed process can take the place of a file by duplicating all of the methods and attributes that file objects have. There are two base functions that have been added to the subprocess.Popen class: Popen.send and Popen._recv, each with two separate implementations, one for Windows and one for Unix based systems. The Windows implementation uses ctypes to access the functions needed to control pipes in the kernel 32 DLL in an asynchronous manner. On Unix based systems, the Python interface for file control serves the same purpose. The different implementations of Popen.send and Popen._recv have identical arguments to make code that uses these functions work across multiple platforms. When calling the Popen._recv function, it requires the pipe name be passed as an argument so there exists the Popen.recv function that passes selects stdout as the pipe for Popen._recv by default. Popen.recv_err selects stderr as the pipe by default. "Popen.recv" and "Popen.recv_err" are much easier to read and understand than "Popen._recv('stdout' ..." and "Popen._recv('stderr' ..." respectively. Since the Popen._recv function does not wait on data to be produced before returning a value, it may return empty bytes. Popen.asyncread handles this issue by returning all data read over a given time interval. The ProcessIOWrapper class uses the asyncread and asyncwrite functions to allow a process to act like a file so that there are no blocking issues that can arise from using the stdout and stdin file objects produced from a subprocess.Popen call. References: [1] [ python-Feature Requests-1191964 ] asynchronous Subprocess http://mail.python.org/pipermail/python-bugs-list/2006-December/ 036524.html [2] Daily Life in an Ivory Basement : /feb-07/problems-with-subprocess http://ivory.idyll.org/blog/feb-07/problems-with-subprocess [3] How can I run an external command asynchronously from Python? - Stack Overflow http://stackoverflow.com/questions/636561/how-can-i-run-an-external- command-asynchronously-from-python [4] 18.1. subprocess - Subprocess management - Python v2.6.2 documentation http://docs.python.org/library/subprocess.html#subprocess.Popen.wait [5] 18.1. subprocess - Subprocess management - Python v2.6.2 documentation http://docs.python.org/library/subprocess.html#subprocess.Popen.kill [6] Issue 1191964: asynchronous Subprocess - Python tracker http://bugs.python.org/issue1191964 [7] Module to allow Asynchronous subprocess use on Windows and Posix platforms - ActiveState Code http://code.activestate.com/recipes/440554/ [8] subprocess.rst - subprocdev - Project Hosting on Google Code http://code.google.com/p/subprocdev/source/browse/doc/subprocess.rst?spec=s… [9] subprocdev - Project Hosting on Google Code http://code.google.com/p/subprocdev [10] Python Subprocess Dev http://subdev.blogspot.com/ Copyright: This P.E.P. is licensed under the Open Publication License; http://www.opencontent.org/openpub/. On Tue, Sep 8, 2009 at 22:56, Benjamin Peterson <benjamin(a)python.org> wrote: > 2009/9/7 Eric Pruitt <eric.pruitt(a)gmail.com>: >> Hello all, >> >> I have been working on adding asynchronous I/O to the Python >> subprocess module as part of my Google Summer of Code project. Now >> that I have finished documenting and pruning the code, I present PEP >> 3145 for its inclusion into the Python core code. Any and all feedback >> on the PEP (http://www.python.org/dev/peps/pep-3145/) is appreciated. > > Hi Eric, > One of the reasons you're not getting many response is that you've not > pasted the contents of the PEP in this message. That makes it really > easy for people to comment on various sections. > > BTW, it seems like you were trying to use reST formatting with the > text PEP layout. Double backquotes only mean something in reST. > > > -- > Regards, > Benjamin >

7 years, 5 months

http://www.pythonlabs.com/logos.html is gone

by Georg Brandl

Which I noticed since it's cited in the BeOpen license we still refer to in LICENSE. Since pythonlabs.com itself is still up, it probably isn't much work to make the logos.html URI work again, but I don't know who maintains that page. cheer, Georg -- Thus spake the Lord: Thou shalt indent with four spaces. No more, no less. Four shall be the number of spaces thou shalt indent, and the number of thy indenting shall be four. Eight shalt thou not indent, nor either indent thou two, excepting that thou then proceed to four. Tabs are right out.

9 years, 3 months

Problems with hex-conversion functions

by Ender Wiggin

Hello everyone. I see several problems with the two hex-conversion function pairs that Python offers: 1. binascii.hexlify and binascii.unhexlify 2. bytes.fromhex and bytes.hex Problem #1: bytes.hex is not implemented, although it was specified in PEP 358. This means there is no symmetrical function to accompany bytes.fromhex. Problem #2: Both pairs perform the same function, although The Zen Of Python suggests that "There should be one-- and preferably only one --obvious way to do it." I do not understand why PEP 358 specified the bytes function pair although it mentioned the binascii pair... Problem #3: bytes.fromhex may receive spaces in the input string, although binascii.unhexlify may not. I see no good reason for these two functions to have different features. Problem #4: binascii.unhexlify may receive both input types: strings or bytes, whereas bytes.fromhex raises an exception when given a bytes parameter. Again there is no reason for these functions to be different. Problem #5: binascii.hexlify returns a bytes type - although ideally, converting to hex should always return string types and converting from hex should always return bytes. IMO there is no meaning of bytes as an output of hexlify, since the output is a representation of other bytes. This is also the suggested behavior of bytes.hex in PEP 358 Problems #4 and #5 call for a decision about the input and output of the functions being discussed: Option A : Strict input and output unhexlify (and bytes.fromhex) may only receives string and may only return bytes hexlify (and bytes.hex) may only receives bytes and may only return strings Option B : Robust input and strict output unhexlify (and bytes.fromhex) may receive bytes and strings and may only return bytes hexlify (and bytes.hex) may receive bytes or strings and may only return strings Of course we may also consider a third option, which will allow the return type of all functions to be robust (perhaps specified in a keyword argument), but as I wrote in the description of problem #5, I see no sense in that. Note that PEP 3137 describes: "... the more strict definitions of encoding and decoding in Python 3000: encoding always takes a Unicode string and returns a bytes sequence, and decoding always takes a bytes sequence and returns a Unicode string." - suggesting option A. To repeat problems #4 and #5, the current behavior does not match any option: * The return type of binascii.hexlify should be string, and this is not the current behavior. As for the input: * Option A is not the current behavior because binascii.unhexlify may receive both input types. * Option B is not the current behavior because bytes.fromhex does not allow bytes as input. To fix these issues, three changes should be applied: 1. Deprecate bytes.fromhex. This fixes the following problems: #4 (go with option B and remove the function that does not allow bytes input) #2 (the binascii functions will be the only way to "do it") #1 (bytes.hex should not be implemented) 2. In order to keep the functionality that bytes.fromhex has over unhexlify, the latter function should be able to handle spaces in its input (fix #3) 3. binascii.hexlify should return string as its return type (fix #5)

9 years, 8 months

Re: [Python-Dev] [PEP 3148] futures - execute computations asynchronously

by P.J. Eby

At 10:59 AM 3/7/2010 -0800, Jeffrey Yasskin wrote: >So is it that you just don't like the idea of blocking, and want to >stop anything that relies on it from getting into the standard library? Um, no. As I said before, call it a "parallel task queue" or "parallel task manager" or something to that general effect and I'm on board. It may not be in the Zen of Python, but ISTM that names should generally follow use cases. It is something of a corollary to "one obvious way to do it", in that if you see something whose name matches what you want to do, then it should be obvious that that's the way in question. ;-) The use cases for "parallel task queues", however, are a subset of those for "futures" in the general case. Since the proposed module addresses most of the former but very little of the latter, calling it futures is inappropriate. Specifically, it's: 1. Confusing to people who don't know what futures are (see e.g R.D. Murray's post), and 2. Underpowered for people who expect/want a more fully-featured futures system along the lines of E or Deferreds. It seems that the only people for whom it's an intuitively correct description are people who've only had experience with more limited futures models (like Java's). However, these people should not have a problem understanding the notion of parallel task queueing or task management, so changing the name isn't really a loss for them, and it's a gain for everybody else. > Given the set_result and set_exception methods, it's pretty > straightforward to fill in the value of a future from something > that isn't purely computational. Those are described as "internal" methods in the PEP; by contrast, the Deferred equivalents are part of the public API. > Given a way to register "on-done" callbacks with the future, it > would be straightforward to wait for a future without blocking, too. Yes, and with a few more additions besides that one, you might be on the way to an actual competitor for Deferreds. For example: retry support, chaining, logging, API for transparent result processing, coroutine support, co-ordination tools like locks, sempaphores and queues, etc. These are all things you would very likely want or need if you actually wanted to write a program using futures as *your main computational model*, vs. just needing to toss out some parallel tasks in a primarily synchronous program. Of course, Deferreds are indeed overkill if all you're ever going to want is a few parallel tasks, unless you're already skilled in using Twisted or some wrapper for it. So, I totally support having a simple task queue in the stdlib, as there are definitely times I would've used such a thing for a quick script, if it were available. However, I've *also* had use cases for using futures as a computational model, and so that's what I originally thought this PEP was about. After the use cases were clarified, though, it seems to me that *calling* it futures is a bad idea, because it's really just a nice task queuing system. I'm +1 on adding a nice task queuing system, -1 on calling it by any other name. ;-)

10 years

Fwd: Broken link to download (Mac OS X)

by webmaster＠python.org

Hey all, This seems to happen whenever we do a new release (we've had a couple of emails to webmaster(a)python.org about it since 2.6.5 was released). The main download page for Python has a broken link for the Mac installer (because it hasn't been built yet I assume): http://python.org/download/ The link 404s, with no explanation or alternate link - so for the casual user who wants to install Python 2.6 on Mac OS X they are sorely-out-of-luck. Not being able to provide a mac installer at the same time as other platforms is one thing (and I accept that is unavoidable), breaking the download links for Mac users for unspecified lengths of time is just bad practise. If we create a new stable release without a Mac installer can we at least provide a brief explanation and link to the *previous version* until the new version is ready? All the best, Michael -------- Original Message -------- Subject: Broken link to down Date: Sun, 21 Mar 2010 13:40:36 +0000 From: Ben Hodgson <ben(a)benhodgson.com> To: webmaster(a)python.org Hey there, In case you don't know, the link on http://www.python.org/download/ to the Python 2.6.5 Mac Installer Disk Image (http://www.python.org/ftp/python/2.6.5/python-2.6.5_macosx10.3.dmg) is broken. Cheers, Ben -- Ben Hodgson http://benhodgson.com/

10 years, 1 month

Bug? syslog.openlog using ident "python" by default.

by Sean Reifschneider

I'd appreciate some opinions on this. Personally, I'm in the "the current code is buggy" camp. :-) I can code up the changes to the syslog module if we decide that's the right way to go. Looks like Raymond, Guido, and I are the last ones to do syslog-specific changes to this module in the last 15 years. If you call: from syslog import syslog, openlog syslog('My error message') Something like the following gets logged: Mar 18 05:20:22 guin python: My error message ^^^^^^ Where I'm annoyed by the "python" in the above. This is pulled from the C argv[0]. IMHO, what we really want is the Python sys.argv[0]. Because of this feature, I always have to do the following when I'm using syslog: openlog(os.path.basename(sys.argv[0])) I would propose changing the Python syslog() call to do the C equivalent of: if openlog_hasnt_been_called_before_now: if sys.argv[0]: syslog.openlog(os.path.basename(sys.argv[0])) In other words, if there's a script name and openlog hasn't already been called, call openlog with the basename of the script name. This is effectively what happens in normal C code that calls syslog. Note that the Python syslog.openlog says that the default for ident is "(usually) 'syslog'". The benefit of this change is that you get a more identifiable ident string in Python programs, so when you look at the logs you can tell what script it came from, not just that it came from some Python program. One way of looking at it would be that the syslog module logging "python" as the program name is a bug. The downside I see is that there might be some users doing log scraping depending on this (IMHO, buggy) log ident. Something else just occurred to me though, a nice enhancement would be for openlog() to have a "None" default for ident, something like: orig_openlog = openlog def openlog(ident = None, logopt = 0, facility = LOG_USER) if ident == None: if sys.argv[0]: ident = os.path.basename(sys.argv[0]) else: ident = 'python' orig_openlog(ident, logopt, facility) So you could call openlog and rely on the default ident (sys.argv[0]), and set the logopt and facility. The gory details of why this is occurring are: If you don't call "openlog()" before "syslog()", the system syslog() function calls something similar to: "openlog(basename(argv[0]))", which causes the "ident" of the syslog messages to be "python" rather than the specific program. Thoughts? Thanks, Sean -- "Every increased possession loads us with new weariness." -- John Ruskin Sean Reifschneider, Member of Technical Staff <jafo(a)tummy.com> tummy.com, ltd. - Linux Consulting since 1995: Ask me about High Availability

10 years, 1 month

Google Groups mirror (Was: Bootstrap script for package management tool in Python 2.7)

by anatoly techtonik

On Mon, Mar 29, 2010 at 4:50 PM, Tarek Ziadé <ziade.tarek(a)gmail.com> wrote: > Anatoly, I am now answering only in Distutils-SIG. > > On Mon, Mar 29, 2010 at 3:45 PM, anatoly techtonik <techtonik(a)gmail.com> wrote: > [..] Seems like I start to hate mailing lists even more with all this message duplication and thread following nightmare. Why can't people here create a Google Groups mirror? -- anatoly t.

10 years, 1 month

Request for commit access

by Brian Curtin

Hi all, Having been active in bug triage and patch writing/reviewing since late 2009, it was suggested in the python-dev IRC channel that I request commit access to the repository. I'm primarily a Windows user and have worked with many of the other active contributors to diagnose issues and test patches when they don't have direct access to Windows. Brian Curtin p.s. My contributor form in on file as of 2010-01-31.

10 years, 1 month

Re: [Python-Dev] Decimal <-> float comparisons in py3k.

by P.J. Eby

At 09:58 AM 3/16/2010 -0500, Facundo Batista wrote: >I'm +0 to allow these comparisons, being "Decimal(1) < .3" the same as >"Decimal(1) < Decimal.from_float(.3)" Does Decimal.from_float() use the "shortest decimal representation" approach? If not, it might be confusing if a number that prints as '.1' compares unequal to Decimal('.1').

10 years, 1 month

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Python-Dev March 2010