Python-Dev December 2009

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74 participants
43 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, 11 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, 6 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, 5 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, 9 months

Making loggerClass an attribute of the logger manager?

by Georg Brandl

Hi, recently I had a use case where I wanted to use logging in two completely separate parts of the same process. One of them needs to create instances a specific Logger subclass, while the other is fine with the default loggers. I got around the problem of the unique root node by using two Managers (and then using Manager.getLogger() instead of getLogger()), but I can only set the loggerClass globally. Making the loggerClass configurable per manager would solve the problem for me, and AFAICS since most applications don't use different managers anyway, there should not be any detrimental effects. What do you think? cheers, Georg

10 years, 5 months

Re: [Python-Dev] Question over splitting unittest into a package

by Benjamin Peterson

2009/12/30 Martin (gzlist) <gzlist(a)googlemail.com>: > Hi Benjamin, Hi! > > In rev 74094 of Python, you split the unittest module up, could you > point me at any bug entries or discussion over this revision so I can > catch up? This was mostly a discussion on IRC between Michael Foord and myself. > > As a side-effect you seem to have changed the method of marking a > module as not worth including in a traceback to be no longer > extensible. > > Before: > <http://svn.python.org/view/python/trunk/Lib/unittest.py?view=markup&pathrev…> > > A global was set at the top of the module: > > __unittest = 1 > > Which is then checked for when constructing traceback output: > > def _is_relevant_tb_level(self, tb): > return '__unittest' in tb.tb_frame.f_globals > > After: > <http://svn.python.org/view/python/trunk/Lib/unittest/__init__.py?revision=7…> > > def _is_relevant_tb_level(self, tb): > globs = tb.tb_frame.f_globals > is_relevant = '__name__' in globs and \ > globs["__name__"].startswith("unittest") > del globs > return is_relevant > > Only packages actually named "unittest" can be excluded. > > What is now the prefered method of marking a module as test-internal? > Overriding the leading-underscore _is_relevant_tb_level method? How > can this be done cooperatively by different packages? When I made that change, I didn't know that the __unittest "hack" was being used elsewhere outside of unittest, so I felt fine replacing it with another. While I still consider it an implementation detail, I would be ok with exposing an "official" API for this. Perhaps __unittest_ignore_traceback? > I would have CCed a mailinglist with this question but don't like > getting yelled at for posting on the wrong one, please feel free to do > so with your reply if you feel it's appropriate (the CCing, not the > yelling). python-dev is perfect for this discussion. -- Regards, Benjamin

10 years, 6 months

Pronouncement on PEP 389: argparse?

by Steven Bethard

So there wasn't really any more feedback on the last post of the argparse PEP other than a typo fix and another +1. http://www.python.org/dev/peps/pep-0389/ Can I get a pronouncement? Here's a summary of the responses. (Please correct me if I misinterpreted anyone.) * Floris Bruynooghe +1 * Brett Cannon +1 * Nick Coghlan +1 * Michael Foord +1 * Yuval Greenfield +1 * Doug Hellmann +1 * Kevin Jacobs +1 * Paul Moore +1 * Jesse Noller +1 * Fernando Perez +1 * Jon Ribbens +1 * Vinay Sajip +1 * Barry Warsaw +1 * Antoine Pitrou -0 * Martin v. Löwis -0 * M.-A. Lemburg -1 Note that I've interpreted those who were opposed to the deprecation of getopt as -0 since the PEP no longer proposes that, only the deprecation of optparse. (People who opposed optparse's deprecation are still -1.) If there's any other information that would be helpful for a pronouncement, please let me know. Steve -- Where did you get that preposterous hypothesis? Did Steve tell you that? --- The Hiphopopotamus

10 years, 6 months

Proposing PEP 345 : Metadata for Python Software Packages 1.2

by Tarek Ziadé

Hi, On behalf of the Distutils-SIG, I would like to propose to addition of PEP 345 (once and *if* PEP 386 is accepted). It's the metadata v1.2: http://www.python.org/dev/peps/pep-0345/ PEP 345 was initiated a while ago by Richard Jones, and reworked since then together with PEP 386, at Pycon last year and in Distutils-SIG. The major enhancements are: - being able to express dependencies on other *distributions* names, rather than packages names or modules names. This enhancement comes from Setuptools and has been used successfully for years by the community. - being able to express some fields which values are specific to some platforms. For example, being able to define "pywin32" as a dependency *only* on win32. This enhancement will allow any tool to query PyPI and to get the metadata for a particular execution context, without having to download, build, or install the project itself. - being able to provide a list of browsable URLs for the project, like a bug tracker, a repository etc, in addition to the home url. This will allow UIs like PyPI to display a list of URLs for a project. A side-effect will be that a project maintainer will be able to drive its end users to the right places when they need to find detailed documentation or provide some feedback. This enhancement was driven by the discussions about the rating/comment system at PyPI on catalog-sig. We believe that having PEP 386 and PEP 345 accepted will be a major improvement for the Python packaging eco-system. The next PEP in the series we are working on is PEP 376. As a side note, I would really like to see them (hopefully) accepted before the first beta of Python 2.7 so we can add these features in 2.7/3.2 and start to work on third-party tools (Distribute, Pip, a standalone version of Distutils for 2.6/2.5, etc..) to get ready to support them by the time 2.7 final is out. Regards Tarek -- Tarek Ziadé | http://ziade.org

10 years, 6 months

Providing support files to assist 3.x extension authors

by Case Vanhorsen

Hello, When I ported gmpy (Python to GMP multiple precision library) to Python 3.x, I began to use PyLong_AsLongAndOverflow frequently. I found the code to slightly faster and cleaner than using PyLong_AsLong and checking for overflow. I looked at making PyLong_AsLongAndOverflow available to Python 2.x. http://bugs.python.org/issue7528 includes a patch that adds PyLong_AsLongAndOverflow to Python 2.7. I also included a file (py3intcompat.c) that can be included with an extension's source code and provides PyLong_AsLongAndOverflow to earlier versions of Python 2.x. In the bug report, I suggested that py3intcompat.c could be included in the Misc directory and be made available to extension authors. This follows the precedent of pymemcompat.h. But there may be more "compatibility" files that could benefit extension authors. Mark Dickinson suggested that I bring the topic on python-dev. Several questions come to mind: 1) Is it reasonable to provide backward compatibility files (either as .h or .c) to provide support to new API calls to extension authors? 2) If yes, should they be included with the Python source or distributed as a separate entity? (2to3 and/or 3to2 projects, a Wiki page) 3) If not, and extension authors can create their own compatibility files, are there any specific attribution or copyright messages that must be included? (I assuming the compatibility was done by extracting the code for the new API and tweaking it to run on older versions of Python.) Thanks in advance for your attention, Case Van Horsen

10 years, 6 months

First draft of "sysconfig"

by Tarek Ziadé

Hello, A while ago I've proposed to refactor the APIs that provides access to the installation paths and configuration variables at runtime into a single module called "sysconfig", and make it easier for all implementations to work with them. I've started a branch and worked on it, and I'd like to ask here for some feedback. And in particular from Jython and IronPython people because they would probably need to work in that file for their implementation and/or propose things to add. My understanding is that we have people like Phillip (Jenvey), Michael F., Frank W. in this list so they can comment directly and I don't need to cross-post this mail elsewhere. == Installation schemes == First, the module contains the installation schemes for each platform CPython uses. An install scheme is a mapping where the key is the "code" name for a directory, and the value the path of that directory, with some $variable that can be expanded. Install schemes are stored in a private mapping, where the keys are usually the value of os.name, and the value, the mapping I've mentionned earlier. So, for example, the paths for win32 are: _INSTALL_SCHEMES = { ... 'nt': { 'stdlib': '$base/Lib', 'platstdlib': '$base/Lib', 'purelib': '$base/Lib/site-packages', 'platlib': '$base/Lib/site-packages', 'include': '$base/include', 'platinclude': '$base/include', 'scripts': '$base/Scripts', 'data' : '$base', }, ... } where each key corresponds to a directory that contains some Python files: - stdlib : root of the standard library - platstdlib: root of platform-specific elements of the standard library - purelib: the site-packages directory for pure python modules - platlib: the site-packages directory for platform-specific modules - include: the include dir - platinclude: the include dir for platform-specific files - scripts: the directory where scripts are added - data: the directory where data file are added All these directory are read and used by: - distutils when a package is installed, so the install command can dispatch files in the right place - site.py, when Python is initialized IOW, any part of the stdlib can use these paths to locate and work with Python files. The public APIs are: * get_path_names() : returns a list of the path names ("stdlib", "platstdlib", etc.) * get_paths(scheme, vars) : Returns a mapping containing an install scheme. - "scheme" is the name of the scheme, if not provided will get the default scheme of the current platform - vars is an optonal mapping that can provide values for the various $variables. Notice that they all have default values, for example $base == sys.prefix. for example: get_paths('nt') * get_path(name, scheme, vars): Returns one path corresponding to the scheme. for example : get_paths('stdlib', 'nt') Those API are generic, but maybe we could add specific APIs like: * get_stdlib_path('nt') These API are basically a refactoring of what already exist in distutils/command/install.py == Configuration variables == distutils.sysconfig currently provides some APIs to read values from files like Makefile and pyconfig.h. These API have been placed in the global sysconfig module: * get_config_vars(): return a dictionary of all configuration variables relevant for the current platform. * get_config_var(name): Return the value of a single variable * get_platform(): Return a string that identifies the current platform. (this one is used by site.py for example) * get_python_version() : return the short python version (sys.version[:3]) -- this one could probably go away but is useful because that's the marker used by Python in some paths. == code, status, next steps == The code of the module can be viewed here, it's a revamp of distutils.sysconfig: http://svn.python.org/view/*checkout*/python/branches/tarek_sysconfig/Lib/s… I've refactored distutils/ and site.py so they work with this new module, and added deprecation warnings in distutils.sysconfig. All tests pass in the branch, but note that the code is still using the .h and Makefile files. This will probably be removed later in favor of a static _sysconfig.py file generated when Python is built, containing the variables sysconfig reads. I'll do this second step after I get some feedback on the proposal. Regards Tarek -- Tarek Ziadé | http://ziade.org

10 years, 6 months

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Python-Dev December 2009