Mailman 3 July 2019 - Python-Dev

Comparing dict.values()
by Kristian Klette July 29, 2019

July 29, 2019

Hi! During the sprints after EuroPython, I made an attempt at adding support for comparing the results from `.values()` of two dicts. Currently the following works as expected: ``` d = {'a': 1234} d.keys() == d.keys() d.items() == d.items() ``` but `d.values() == d.values()` does not return the expected results. It always returns `False`. The symmetry is a bit off. In the bug trackers[0] and the Github PR[1], I was asked to raise the issue on the python-dev mailing list to find a … [View More]

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[RELEASE] Python 3.8.0b3 is now available for testing
by Łukasz Langa July 29, 2019

July 29, 2019

This time without delays, I present you Python 3.8.0b3: https://www.python.org/downloads/release/python-380b3/ <https://www.python.org/downloads/release/python-380b3/> This release is the third of four planned beta release previews. Beta release previews are intended to give the wider community the opportunity to test new features and bug fixes and to prepare their projects to support the new feature release. The next pre-release of Python 3.8 will be 3.8.0b4, the last beta release, … [View More]

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🍝 New keyword in bpo: `newcomer friendly`
by Mariatta July 29, 2019

July 29, 2019

🍝 copy-pasta from core-mentorship mailing list. There is now a “newcomer friendly” keyword in bpo. My hope is that going forward, we can tag issues that are suitable for first time contributors with this keyword. It would be great for experienced contributors already familiar with our workflow to not work on issues tagged with newcomer friendly and leave that to new contributors. I’ve added the keyword to Devguide’s Triaging section, with additional guideline of what can be tagged as … [View More]

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Summary of Python tracker Issues
by Python tracker July 26, 2019

July 26, 2019

ACTIVITY SUMMARY (2019-07-19 - 2019-07-26) Python tracker at https://bugs.python.org/ To view or respond to any of the issues listed below, click on the issue. Do NOT respond to this message. Issues counts and deltas: open 7127 (+16) closed 42314 (+42) total 49441 (+58) Open issues with patches: 2882 Issues opened (40) ================== #37633: Py_CompileString and PyParser_SimpleParseString not exported i https://bugs.python.org/issue37633 opened by pyscripter #37634: doc: "… [View More]

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Fwd: Re: Comparing dict.values()
by David Mertz July 26, 2019

July 26, 2019

On Thu, Jul 25, 2019 at 4:35 AM Petr Viktorin <encukou(a)gmail.com> wrote: > It's not the equality operator that errors: `==` means element-wise > comparison in Numpy. The error would come from a conversion of the array > to bool: > > >>> numpy.array([1, 2, 3]) == numpy.array([1, 3, 4]) > array([ True, False, False]) > > >>> if numpy.array([ True, False, False]): > ... print('Same!') > ... > Traceback (most recent call last): > … [View More] File "<stdin>", line 1, in <module> > ValueError: The truth value of an array with more than one element is > ambiguous. Use a.any() or a.all() > This is true of course. I was being overly concise, but `arr1 == arr2` does not itself (currently) raise any exception. It's only `if arr1==arr2` that does. But what NumPy does is return a "special" object that has some methods to convert it into a boolean in different ways. We COULD do that with `d1.values() == d2.values()` in principle. This "DictValuesComparison" object could have methods like `.equal_as_set()` and `.equal_as_list()`. However, that's a lot of machinery for very little gain. In contrast, a NumPy boolean array is useful for lots of purposes, and it is something we want independently to have around. Mostly it's a great way of indexing into another list of numeric elements. But it also can be used in some less common, but not uncommon ways. A hypothetical DictValuesComparison object would have nearly no use other than avoiding wrapping d.values() in list(), which we can already do fine. Sure, maybe that rare case could be made a little faster with this custom machinery, but it doesn't feel worthwhile to me. Therefore, I think the exception with guidance in the message should happen at actual equality (or inequality) comparison time, not when casting to a boolean context. Numpy currently returns False when `==` “doesn't make sense”, but > apparently has plans to change that: > > >>> numpy.array([1, 2, 3]) == numpy.array([1, 2]) > __main__:1: DeprecationWarning: elementwise comparison failed; this will > raise an error in the future. > False > > >>> numpy.array([1, 2, 3]) == numpy.array(['a', 'b']) > __main__:1: FutureWarning: elementwise comparison failed; returning > scalar instead, but in the future will perform elementwise comparison > False > This is very interesting! I did not know about this planned change. That NumPy will start raising exceptions on equality comparison adds a little bit of support for my suggestion, I think. > > So, a helpful error message including something like "Cannot compare > > dict.values directly, consider converting to sets / lists / sorted > > lists before comparing" ? > -- Keeping medicines from the bloodstreams of the sick; food from the bellies of the hungry; books from the hands of the uneducated; technology from the underdeveloped; and putting advocates of freedom in prisons. Intellectual property is to the 21st century what the slave trade was to the 16th. [View Less]

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Python 3.7.4, Visual Studio versions for building modules from source
by Kacvinsky, Tom July 23, 2019

July 23, 2019

HI, Not sure if this is the right place to ask, but I am trying to build pywin32-224 from source for Python 3.7.4. I think this might be the right list as this seems to be a generic problem I am having, but I want to focus on one particular module. First, I know I could get this via 'pip install', but I want to build from source to see what it takes in terms of the Windows SDK and Visual Studio versions for some other work I am doing. I am using Python 3.7.4, and I have Visual Studio 2017 … [View More]

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Replacing 4 underscores with a $ sign, idea for a PEP
by karld＠beholdingeye.com July 23, 2019

July 23, 2019

Hello good people of Python Dev! My name is Karl and I have been a Python user since 2010, professionally since 2015. I belong to the "novice, non-technical" group of users, having got my start with programming in the 1990s using HyperTalk, possibly the easiest language of all, with the most English-like syntax. My move to Python in 2010 resulted from my move to Linux at that time. The "easy syntax, almost like pseudo code" assessment that is often repeated about Python was a big factor in … [View More]

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The order of operands in the comparison
by Serhiy Storchaka July 22, 2019

July 22, 2019

Usually the order of operands of the == operator does not matter. bool(a == b) should return the same as bool(b == a). Correct __eq__ should look like: def __eq__(self, other): if not know how to compare with other: return NotImplemented return the result of comparison But we work with non-perfect code written by non-perfect people. __eq__() can return False instead of NotImplemented for comparison with different type (it is not the worst case, in worst … [View More]

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Sphinx is blocking merges
by Terry Reedy July 21, 2019

July 21, 2019

One of the required CI tests is a Travis doc build, even if a PR does not touch any doc file. The following failure appears to be deterministic on master and 3.8. A 3.7 backport passed. It has happened multiple times on multiple PRs today. Example: https://travis-ci.org/python/cpython/jobs/561700698 The failure is ''' Warning, treated as error: [distutils/examples:267] "`" found in "This is the description of the ``foobar`` package." ''' See https://bugs.python.org/issue37644 -- Terry Jan Reedy

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Long-term deprecation policy
by Jeroen Demeyer July 19, 2019

July 19, 2019

I have seen multiple discussions where somebody wants to deprecate a useless function but somebody else complains that we cannot do that because the function in question cannot be removed (because of backwards compatibility). See https://bugs.python.org/issue29548 for an example. We currently have a deprecation policy saying that functions deprecated in version N cannot be removed before version N+2. That's a reasonable policy but some deprecation purists insist that it MUST (instead of … [View More]

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