Mailman 3 January 2021 - docs

[issue30295] msvcrt SetErrorMode not documented
by Giampaolo Rodola' 06 Mar '21

06 Mar '21

New submission from Giampaolo Rodola': Also SEM_FAILCRITICALERRORS and other SEM_constants. They should as setting error mode on Windows for console applications is a pretty common use case (in fact ./Lib/test/libregrtest/setup.py uses it). ---------- assignee: docs@python components: Documentation messages: 293189 nosy: docs@python, giampaolo.rodola priority: normal severity: normal status: open title: msvcrt SetErrorMode not documented versions: Python 3.4, Python 3.5, Python 3.6, Python 3.7 _______________________________________ Python tracker <report(a)bugs.python.org> <http://bugs.python.org/issue30295> _______________________________________

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[issue8557] subprocess portability issue
by Dave Abrahams 05 Mar '21

05 Mar '21

New submission from Dave Abrahams <dave(a)boostpro.com>: On POSIX systems, the PATH environment variable is always used to look up directory-less executable names passed as the first argument to Popen(...), but on Windows, PATH is only considered when shell=True is also passed. Actually I think it may be slightly weirder than that when shell=False, because the following holds for me: C:\>rem ##### Prepare minimal PATH ##### C:\>set "PATH=C:\Python26\Scripts;C:\Python26;C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem" C:\>rem ##### Prepare a minimal, clean environment ##### C:\>virtualenv --no-site-packages e:\zzz New python executable in e:\zzz\Scripts\python.exe Installing setuptools................done. C:\>rem ##### Show that shell=True makes the difference in determining whether PATH is respected ##### C:\>python Python 2.6.5 (r265:79096, Mar 19 2010, 18:02:59) [MSC v.1500 64 bit (AMD64)] on win32 Type "help", "copyright", "credits" or "license" for more information. >>> import subprocess >>> subprocess.Popen(['python', '-c', 'import sys; print sys.executable']) <subprocess.Popen object at 0x0000000001DBE080> >>> C:\Python26\python.exe >>> subprocess.Popen(['python', '-c', 'import sys; print sys.executable'], env={'PATH':r'e:\zzz\Scripts'}) <subprocess.Popen object at 0x0000000001F05A90> >>> C:\Python26\python.exe >>> subprocess.Popen(['python', '-c', 'import sys; print sys.executable'], env={'PATH':r'e:\zzz\Scripts'}, shell=True) <subprocess.Popen object at 0x0000000001F05B00> >>> e:\zzz\Scripts\python.exe That is, it looks like the environment at the time Python is invoked is what counts unless I pass shell=True. I don't even seem to be able to override this behavior by changing os.environ: you can clear() it and pass env={} and subprocess.Popen(['python']) still succeeds. This is a very important problem for portable code and one that took me hours to suss out. I think: a) the current behavior needs to be documented b) it needs to be fixed if possible c) otherwise, shell=True should be the default ---------- assignee: docs@python components: Documentation messages: 104422 nosy: dabrahams, docs@python priority: normal severity: normal status: open title: subprocess portability issue type: behavior versions: Python 2.6 _______________________________________ Python tracker <report(a)bugs.python.org> <http://bugs.python.org/issue8557> _______________________________________

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[issue16272] C-API documentation clarification for tp_dictoffset
by Chris Colbert 05 Mar '21

05 Mar '21

New submission from Chris Colbert: The documentation of the tp_dictoffset is a bit unclear when describing the responsibilities of a base type with a nonzero tp_dictoffset. http://docs.python.org/c-api/typeobj.html I feel there should some statement to the effect of: """ If a type defines a nonzero tp_dictoffset, that type is responsible for defining a `__dict__` slot as part of the tp_getset structures. Failure to do so will result in the dict being inaccesible from Python via `obj.__dict__` from instances of the type or subtypes. """ The reasoning is twofold: 1) `PyType_Ready` does not add the default getset members like `type_new` does. This prevents the instances of the type itself from retrieving `obj.__dict__` 2) `type_new` will provide the default `subtype_dict` getset member for subclasses, but this calls `get_builtin_base_with_dict` which will resolve to the most base type which is not heap allocated; in this case, the C type. Since this type has no `__dict__` getset member, the lookup fails. Adding a bit of verbage about this "gotcha" would likely save some headaches in the future. ---------- assignee: docs@python components: Documentation messages: 173222 nosy: Chris.Colbert, docs@python priority: normal severity: normal status: open title: C-API documentation clarification for tp_dictoffset versions: Python 2.6, Python 2.7, Python 3.1, Python 3.2, Python 3.3, Python 3.4, Python 3.5 _______________________________________ Python tracker <report(a)bugs.python.org> <http://bugs.python.org/issue16272> _______________________________________

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[issue39375] Document os.environ[x] = y and os.putenv() as thread unsafe
by Gregory P. Smith 04 Mar '21

04 Mar '21

New submission from Gregory P. Smith <greg(a)krypto.org>: The underlying API calls made by os.putenv() and os.environ[name] = value syntax are not thread safe on POSIX systems. POSIX _does not have_ any thread safe way to access the process global environment. In a pure Python program, the GIL prevents this from being an issue. But when embedded in a C/C++ program or using extension modules that launch their own threads from C, those threads could also make the invalid assumption that they can safely _read_ the environment. Which is a race condition when a Python thread is doing a putenv() at the same time. We should document the danger. CPython's os module snapshots a copy of the environment into a dict at import time (during CPython startup). But os.environ[] assignment and os.putenv() modify the actual process global environment in addition to updating this dict. (If an embedded interpreter is launched from a process with other threads already running, even that initial environment reading could be unsafe if the larger application has a thread that wrongly assumes it has exclusive environment access) For people modifying os.environ so that the change is visible to child processes, we can recommend using the env= parameter on subprocess API calls to supply a new environment. A broader issue of should we be modifying the process global environment state at all from os.putenv() and os.environ[] assignment still exists. I'll track that in another issue (to be opened). ---------- assignee: docs@python components: Documentation messages: 360221 nosy: docs@python, gregory.p.smith priority: normal severity: normal status: open title: Document os.environ[x] = y and os.putenv() as thread unsafe versions: Python 2.7, Python 3.7, Python 3.8, Python 3.9 _______________________________________ Python tracker <report(a)bugs.python.org> <https://bugs.python.org/issue39375> _______________________________________

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[issue29829] Documentation lacks clear warning of subprocess issue with pythonw
by Steve Barnes 04 Mar '21

04 Mar '21

New submission from Steve Barnes: When running under pythonw, or pyinstaller with the -w flag, modules that use subprocess calls such as popen, run, etc. will crash if the default `stdout=None, stderr=None` behaviour is used rather than PIPE. This is an obscure problem which is very hard to debug yet there is no warning in the documentation on this. I would like to suggest adding a :warning:`stdout=None, stderr=None` must not be used in any of the calls in this module when running under pythonw due to the lack of sys.stdout & sys.stderr in that case. Please use `stdout=PIPE, stderr=PIPE` instead. A patch against the default branch would be: diff -r 4243df51fe43 Doc/library/subprocess.rst --- a/Doc/library/subprocess.rst Fri Feb 10 14:19:36 2017 +0100 +++ b/Doc/library/subprocess.rst Thu Mar 16 16:56:24 2017 +0000 @@ -33,6 +33,13 @@ function for all use cases it can handle. For more advanced use cases, the underlying :class:`Popen` interface can be used directly. +.. warning:: Do not use default parameters on Windows with pythonw. + + As pythonw deletes `sys.stdout` & `sys.stderr` the use of the default + parameters, `stdout=None, stderr=None,`, which defaults to being + `stdout=sys.stdout, stderr=sys.stderr,` may cause unexpected crashes + it is recommended to use `stdout=PIPE, stderr=PIPE,` instead. + The :func:`run` function was added in Python 3.5; if you need to retain compatibility with older versions, see the :ref:`call-function-trio` section. ---------- assignee: docs@python components: Documentation messages: 289722 nosy: Steve Barnes, docs@python priority: normal severity: normal status: open title: Documentation lacks clear warning of subprocess issue with pythonw type: behavior versions: Python 2.7, Python 3.6, Python 3.7 _______________________________________ Python tracker <report(a)bugs.python.org> <http://bugs.python.org/issue29829> _______________________________________

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[issue12594] Docs for py3k still refer to "MacPython 2.5 folder"
by Christoph Schindler 04 Mar '21

04 Mar '21

New submission from Christoph Schindler <hop(a)30hopsmax.at>: In http://docs.python.org/py3k/using/mac.html#getting-and-installing-macpython and http://docs.python.org/py3k/using/mac.html#distributing-python-applications… . ---------- assignee: docs@python components: Documentation messages: 140744 nosy: docs@python, hop priority: normal severity: normal status: open title: Docs for py3k still refer to "MacPython 2.5 folder" versions: Python 3.1, Python 3.2 _______________________________________ Python tracker <report(a)bugs.python.org> <http://bugs.python.org/issue12594> _______________________________________

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[issue39199] Improve the AST documentation
by Pablo Galindo Salgado 03 Mar '21

03 Mar '21

New submission from Pablo Galindo Salgado <pablogsal(a)gmail.com>: The AST docs need some love as they can be a bit obscure to someone new to the module. Improvements to be considered in this issue: * Document all available nodes (as of 3.8 and not deprecated ones). This helps to know what classes to consider when implementing methods for the visitors. * Add some short practical examples for the visitors: one to query an AST and another to modify it. ---------- assignee: docs@python components: Documentation messages: 359235 nosy: docs@python, pablogsal priority: normal severity: normal status: open title: Improve the AST documentation versions: Python 3.9 _______________________________________ Python tracker <report(a)bugs.python.org> <https://bugs.python.org/issue39199> _______________________________________

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[issue24650] Error in yield expression documentation
by swanson 27 Feb '21

27 Feb '21

New submission from swanson: https://docs.python.org/3/reference/expressions.html in 6.2.9. Yield expressions end of 1st paragraph: "Using a yield expression in a function’s body causes that function to be a generator." NO! As the very next sentence explains, a generator is what's returned by such a function, not the function itself. Basically, it should be sufficient to add the word "function" to the end of that sentence: "... generator function." However, this error does NOT exist in 3.0 to 3.2 - just in 3.3 to 3.6, so I suggest just using the same wording as 3.0 to 3.2: "Using a yield expression in a function definition is sufficient to cause that definition to create a generator function instead of a normal function." ---------- assignee: docs@python components: Documentation messages: 246841 nosy: docs@python, swanson priority: normal severity: normal status: open title: Error in yield expression documentation versions: Python 3.3, Python 3.4, Python 3.5, Python 3.6 _______________________________________ Python tracker <report(a)bugs.python.org> <http://bugs.python.org/issue24650> _______________________________________

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[issue29045] Outdated C api doc about Windows error
by Xiang Zhang 26 Feb '21

26 Feb '21

New submission from Xiang Zhang: https://docs.python.org/3.7/c-api/exceptions.html#c.PyErr_SetFromWindowsErr… it stills refers to PyErr_SetFromWindowsErrWithFilenameObject but this function doesn't exist since Py3.4. I didn't find when and why it's deleted. And https://docs.python.org/3.4/c-api/exceptions.html#c.PyErr_SetFromWindowsErr raises OSError instead of WindowsError. ---------- assignee: docs@python components: Documentation messages: 283814 nosy: docs@python, xiang.zhang priority: normal severity: normal status: open title: Outdated C api doc about Windows error versions: Python 3.5, Python 3.6, Python 3.7 _______________________________________ Python tracker <report(a)bugs.python.org> <http://bugs.python.org/issue29045> _______________________________________

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[issue24045] Behavior of large returncodes (sys.exit(nn))
by Ethan Furman 26 Feb '21

26 Feb '21

New submission from Ethan Furman: Not sure if this is a bug, or just One of Those Things: sys.exit(large_value) can wrap around if the value is too large, but this is O/S dependent. linux (ubuntu 14.04) $ python Python 2.7.8 (default, Oct 20 2014, 15:05:29) [GCC 4.9.1] on linux2 Type "help", "copyright", "credits" or "license" for more information. --> import sys --> sys.exit(256) $ echo $? 0 $ python Python 2.7.8 (default, Oct 20 2014, 15:05:29) [GCC 4.9.1] on linux2 Type "help", "copyright", "credits" or "license" for more information. --> import sys --> sys.exit(257) $ echo $? 1 M$ (Windows 7) > python Python 2.7... --> import sys --> sys.exit(65535) > echo %errorlevel% 65535 > python Python 2.7... --> import sys --> sys.exit(100000) > echo %errorlevel% 100000 Perhaps a minor doc update that talks about return codes and why they might not be exactly what was given to Python? ---------- assignee: docs@python messages: 241903 nosy: docs@python, ethan.furman priority: normal severity: normal status: open title: Behavior of large returncodes (sys.exit(nn)) versions: Python 2.7, Python 3.5 _______________________________________ Python tracker <report(a)bugs.python.org> <http://bugs.python.org/issue24045> _______________________________________

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