🌐 Mailman 3 July 2019 - Python-list - python.org

Modify setup
by couldbeworse01＠protonmail.com July 30, 2019

July 30, 2019

Good morning, I have uninstalled and reinstalled different versions of Python, and continue to get the "modify setup" box when I try to open. Is there something I'm doing wrong? Sent from ProtonMail mobile

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Xml File Error
by Dipangi Shah July 30, 2019

July 30, 2019

Hi, import os from xml.etree import ElementTree file_name = 'Users.xml' full_file = os.path.abspath(os.path.join('data', file_name)) print(full_file) with above code, path is successfully printed as "C:\Users\Evosys\PycharmProjects\Python Level1\data\Users.xml" but when I add below 2 lines, there is an error saying "FileNotFoundError: [Errno 2] No such file or directory: 'C:\\Users\\Evosys\\PycharmProjects\\Python Level1\\data\\Users.xml' dom = ElementTree.parse(full_file,None) print(dom) Can you suggest to me why I am facing the error? -- Regards, Dipangi Shah

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how to generate a standard email form by default OS mail client?
by dmitrey15＠gmail.com July 30, 2019

July 30, 2019

Hello, is Python capable of generating a email form (from standard data - address, topic, string message) with raising it by a default OS email client, e.g. Thunderbird? User would like to have a possibility to review/modify email content inside the OS email client window before sending it. Raising gmail.com GUI form also could be a solution. Thank you in advance, D.

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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, currently scheduled for 2019-08-26. Call to action We strongly encourage maintainers of third-party Python projects to test with 3.8 during the beta phase and report issues found to the Python bug tracker <https://bugs.python.org/> as soon as possible. While the release is planned to be feature complete entering the beta phase, it is possible that features may be modified or, in rare cases, deleted up until the start of the release candidate phase (2019-09-30). Our goal is have no ABI changes after beta 3 and no code changes after 3.8.0rc1, the release candidate. To achieve that, it will be extremely important to get as much exposure for 3.8 as possible during the beta phase. Please keep in mind that this is a preview release and its use is not recommended for production environments. Last beta coming Beta 4 can only be released if all “Release blocker” and “Deferred blocker” issues on bugs.python.org <http://bugs.python.org/> for 3.8.0 are resolved. Please prioritize those for the next four weeks. Acknowledgements Thanks to our binary builders, Ned and Steve, who were very quick today to get the macOS and Windows installers ready. The Windows story in particular got pretty magical, it’s now really fully automatic end-to-end. Thanks to Victor for vastly improving the reliability of multiprocessing tests since Beta 2. Thanks to Pablo for keeping the buildbots green. - Ł

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Re: Boolean comparison & PEP8
by Michael F. Stemper July 29, 2019

July 29, 2019

On 28/07/2019 19.04, Chris Angelico wrote: > On Mon, Jul 29, 2019 at 9:48 AM Michael Torrie <torriem(a)gmail.com> wrote: >> >> On 7/28/19 5:55 AM, Jonathan Moules wrote: >>> But this appears to be explicitly called out as being "Worse" in PEP8: >>> >>> """ >>> Don't compare boolean values to True or False using ==. >>> >>> Yes: if greeting: >>> No: if greeting == True: >>> Worse: if greeting is True: >>> """ >> >> Yet the recommended solution to the problem of wanting a default >> argument of an empty list is something like this: >> >> def foo(bar=False); >> if bar is False: >> bar = [] >> >> .... >> >> Clearly in this case the expression "not bar" would be incorrect. > > This is a fairly unusual case, though. More commonly, the default > would be None, not False, and "if bar is None:" is extremely well > known and idiomatic. That's certainly how I would have done it until I read your post. But reading it immediately raised the question of why not: def foo( bar=[] ): if len(bar)==0: print( "Pretty short" ) else: print( bar ) return Seems to work just fine. -- Michael F. Stemper Deuteronomy 24:17

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Re: Definite or indefinite article for non-singletons?
by Marko Rauhamaa July 29, 2019

July 29, 2019

Ethan Furman <ethan(a)stoneleaf.us>: > On 07/27/2019 02:10 PM, Chris Angelico wrote: >> When talking about indistinguishable objects, is it correct to talk >> about "the <x>" or "an <x>"? > > Multiple indistinguishable objects are still multiple, so "an". > > Implementation details should only enter the conversation when > specifically discussing the implementation -- so CPython is an > implementation detail while Python is the language. Yes. If the API guarantees singleton-ness (reliable testability through "is"), the correct article is "the", otherwise "an". There is no guarantee that two empty strings are the same object so "an empty string" is the right expression. Now, len(string) return "the length" of the string of "a length" of the string: >>> s = "*"*2000 >>> len(s) 2000 >>> len(s) is len(s) False Here "the length" is the right answer and must be understood as a contraction of the pedantic: "an integer representing the length". So it depends on the context if the relevant equivalence is "is" or "==". Maybe the rule of thumb is that if we are talking about strings, integers and similar things, we should think about it from the point of view of Python's data model (objects; "is"). But when we talk about things like "length", "square root", "sum" or "name", the point of view is the abstractions the objects are standing for ("=="). Marko

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Boolean comparison & PEP8
by Jonathan Moules July 29, 2019

July 29, 2019

Hi List, Lets say I want to know if the value of `x` is bool(True). My preferred way to do it is: if x is True: pass Because this tests both the value and the type. But this appears to be explicitly called out as being "Worse" in PEP8: """ Don't compare boolean values to True or False using ==. Yes: if greeting: No: if greeting == True: Worse: if greeting is True: """ Why? If `x` can also have a value of "1"(str) or 1(int) then in both cases this would be a false positive if I were to do the below as they'll both equate to True: if x: pass The PEP for boolean type (285 - https://www.python.org/dev/peps/pep-0285/) doesn't mention the "is" comparison keyword at all as far as I can tell. What am I missing? Thanks

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ubuntu python 2.7 variations
by Robin Becker July 29, 2019

July 29, 2019

I help maintain apps on a number of machines and recently a bug surfaced which affected some of them using the preppy template module; the bug ended up being the way tokenize worked as in the following ############################# from StringIO import StringIO import tokenize, token L = [] s='i' tokenize.tokenize(StringIO(s.strip()).readline,lambda *a: L.append(a)) print('L=%s' % repr(L)) ############################# Older working machines Python 2.7.15rc1 (default, Nov 12 2018, 14:31:15)\n[GCC 7.3.0] on linux2 L=[(1, 'i', (1, 0), (1, 1), 'i'), (0, '', (2, 0), (2, 0), '')] upgraded machines showing a bug Python 2.7.15+ (default, Nov 27 2018, 23:36:35)\n[GCC 7.3.0] on linux2 L=[(1, 'i', (1, 0), (1, 1), 'i'), (4, '', (1, 1), (1, 2), ''), (0, '', (2, 0), (2, 0), '')] The extra token represents a linefeed; however StringIO('i').readline() doesn't contain a linefeed. so the problem is that parsing a simple string 'i' results in two different parses. On my Arch machines running 2.7.16 I see the original parse. The fix was simple and involved using more robust code. My question is that since the package builders feel able to modify and affect behaviour in such a simple case will they do it randomly elsewhere perhaps leading to other less obvious changes. Should I always be using self build python versions? It seems that ubuntu feels able to provide packages which are rc versions or have a + indicating they're modified. They'll probably argue that this improves things and I shouldn't be using such low level code ....... :( -- Robin Becker

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Definite or indefinite article for non-singletons?
by Chris Angelico July 29, 2019

July 29, 2019

When talking about indistinguishable objects, is it correct to talk about "the <x>" or "an <x>"? Example: def f(s): """Frob a thing. If s is an empty string, frobs all the things. OR If s is the empty string, frobs all the things. """ It's entirely possible that a Python implementation will optimize small strings and thus have exactly one empty string, but it's also entirely possible to have multiple indistinguishable empty strings. Grammatically, is it better to think of empty strings as an entire category of object, and you were passed one from that category ("an empty string"), or to think of zero-length instances of 'str' as being implementation details referring to the one and only Platonic "empty string"? Does it make a difference to usage if the object is mutable? For instance, would you say "the empty string" but "an empty set"? ChrisA

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bool(Enum) should raise ValueError
by Erik Aronesty July 28, 2019

July 28, 2019

I just spend a while tracking down and killing all "if Enum" and "if not Enum" bugs in my code. I was frankly shocked that this didn't raise a ValueError to begin with. Apparently all enums are true/false depending on whether the underlying value is truthy or falsy. Which breaks the abstraction Enum's are trying to achieve because now the user of an Enum has to know "stuff" about the underlying value and how it behaves.

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