Python-Dev September 2012

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85 participants
72 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/)

6 years, 1 month

PEP 423 : naming conventions and recipes related to packaging

by Benoît Bryon

Hi, Here is an informational PEP proposal: http://hg.python.org/peps/file/52767ab7e140/pep-0423.txt Could you review it for style, consistency and content? Additional notes: * Original discussion posted to distutils-sig(a)python.org * started on May 2012 at http://mail.python.org/pipermail/distutils-sig/2012-May/018551.html * continues in June 2012 at http://mail.python.org/pipermail/distutils-sig/2012-June/018641.html * that's why I set "Discussion-To:<distutils-sig(a)python.org>" header. * Original document was edited as a contrib to cpython documentation: * http://bugs.python.org/issue14899 * file history at https://bitbucket.org/benoitbryon/cpython/history/Doc/packaging/packagename… * but it looked like a PEP, so posted to peps(a)python.org... Regards, Benoit (benoitbb on irc.freenode.net)

7 years, 2 months

Point of building without threads?

by Antoine Pitrou

Hello, I guess a long time ago, threading support in operating systems wasn't very widespread, but these days all our supported platforms have it. Is it still useful for production purposes to configure --without-threads? Do people use this option for something else than curiosity of mind? Regards Antoine.

7 years, 7 months

Why no venv in existing directory?

by Stefan H. Holek

Hi All, While trying 3.3 beta I found that I cannot use my favorite virtualenv pattern with pyvenv: $ virtualenv . Installing.....done. $ pyvenv . Error: Directory exists: /Users/stefan/sandbox/foo I appreciate that this behavior is documented and was in the PEP from the start: "If the target directory already exists an error will be raised, unless the --clear or --upgrade option was provided." Still, I am curious what the rationale behind this restriction is. For me, being able to "bless" an existing directory with a virtualenv has always been one of its attractions. Thanks, Stefan -- Stefan H. Holek stefan(a)epy.co.at

7 years, 8 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, 9 months

Testing the tests by modifying the ordering of dict items.

by Mark Shannon

Hi, Python code should not depend upon the ordering of items in a dict. Unfortunately it seems that a number of tests in the standard library do just that. Changing PyDict_MINSIZE from 8 to either 4 or 16 causes the following tests to fail: test_dis test_email test_inspect test_nntplib test_packaging test_plistlib test_pprint test_symtable test_trace test_sys also fails, but this is a legitimate failure in sys.getsizeof() Changing the collision resolution function from f(n) = 5n + 1 to f(n) = n + 1 results in the same failures, except for test_packaging and test_symtable which pass. Finally, changing the seed in unicode_hash() from (implicit) 0 to an arbitrary value (12345678) causes the above tests to fail plus: test_json test_set test_ttk_textonly test_urllib test_urlparse I think this is a real issue as the unicode_hash() function is likely to change soon due to http://bugs.python.org/issue13703. Should I: 1. Submit one big bug report? 2. Submit a bug report for each "failing" test separately? 3. Ignore it, since the tests only fail when I start messing about? Cheers, Mark.

7 years, 9 months

Understanding the buffer API

by Jeff Allen

I'm implementing the buffer API and some of memoryview for Jython. I have read with interest, and mostly understood, the discussion in Issue #10181 that led to the v3.3 re-implementation of memoryview and much-improved documentation of the buffer API. Although Jython is targeting v2.7 at the moment, and 1-D bytes (there's no Jython NumPy), I'd like to lay a solid foundation that benefits from the recent CPython work. I hope that some of the complexity in memoryview stems from legacy considerations I don't have to deal with in Jython. I am puzzled that PEP 3118 makes some specifications that seem unnecessary and complicate the implementation. Would those who know the API inside out answer a few questions? My understanding is this: When a consumer requests a buffer from the exporter it specifies using flags how it intends to navigate it. If the buffer actually needs more apparatus than the consumer proposes, this raises an exception. If the buffer needs less apparatus than the consumer proposes, the exporter has to supply what was asked for. For example, if the consumer sets PyBUF_STRIDES, and the buffer can only be navigated by using suboffsets (PIL-style) this raises an exception. Alternatively, if the consumer sets PyBUF_STRIDES, and the buffer is just a simple byte array, the exporter has to supply shape and strides arrays (with trivial values), since the consumer is going to use those arrays. Is there any harm is supplying shape and strides when they were not requested? The PEP says: "PyBUF_ND ... If this is not given then shape will be NULL". It doesn't stipulate that strides will be null if PyBUF_STRIDES is not given, but the library documentation says so. suboffsets is different since even when requested, it will be null if not needed. Similar, but simpler, the PEP says "PyBUF_FORMAT ... If format is not explicitly requested then the format must be returned as NULL (which means "B", or unsigned bytes)". What would be the harm in returning "B"? One place where this really matters is in the implementation of memoryview. PyMemoryView requests a buffer with the flags PyBUF_FULL_RO, so even a simple byte buffer export will come with shape, strides and format. A consumer (of the memoryview's buffer API) might specify PyBUF_SIMPLE: according to the PEP I can't simply give it the original buffer since required fields (that the consumer will presumably not access) are not NULL. In practice, I'd like to: what could possibly go wrong? Jeff Allen

7 years, 9 months

Tru64 support

by Andrew Svetlov

Unittests for subprocess module has weird comment: We cannot use os.path.realpath to canonicalize the path, since it doesn't expand Tru64 {memb} strings. See bug 1063571. http://hg.python.org/cpython/file/82ae284cd5f1/Lib/test/test_subprocess.py#… is link to comment, http://bugs.python.org/issue1063571 — issue in bugtracker. Is it still up to date? Bug has been created in 2004. I don't see Tru64 in list of available buildbots. Do we need to care about this platform? And how to make sure what existing code works fine for that? Or maybe we can drop support for Tru64 as well as we already does it for, say, VMS? -- Thanks, Andrew Svetlov

7 years, 10 months

Python Bug Day in October

by Éric Araujo

Hi all, The Montreal-Python user group would like to host a bug day on October 27 (to be confirmed) at a partner university in Montreal. It would be cool to do a bug day on IRC like we used to (and in other physical locations if people want to!) to get new contributors and close bugs. What do you think? Cheers

7 years, 11 months

what´s new 3.3

by Kristján Valur Jónsson

Hi there. Not having kept up, I realized I failed to contribute to the What's new thingie. Here's stuff I remember working on and putting in: 1. pickling support for built in iterators (#14288) 2. inter process socket duplication for windows (#14310) 3. Progress callback for gc module (#10576) 4. Faster locking on windows (#15038) DiSome of this should probably be mentioned in the What's new document, even if only in its online version. K

7 years, 12 months

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Python-Dev September 2012