Mailman 3 December 2019 - Python-ideas

lowercase exception names trip-up .
by Matthias Bussonnier Dec. 7, 2019

Dec. 7, 2019

I've been tripped up a couple of time by a few Exception names being lower case both in code and tracebacks. In particular `error` (all lower case) I tend to read `error` as a function instead of a class. According to my non-scientific grep-foo, I find that ~ 300 descendant from Exceptions start with an upper case: ~/dev/cpython[master ✗] $ rg '^[ ]*class [A-Z][a-zA-Z]+\(' | grep Excep | wc -l 333 18 of those are `Error` uppercase: ~/dev/cpython[master ✗] $ rg '^[ ]*class Error\(' |… [View More]

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Argumenting in favor of first()
by Juancarlo Añez Dec. 6, 2019

Dec. 6, 2019

I just found this code: def get_product_item(jsonld_items): for item in jsonld_items: if item['@type'] == 'Product': return item else: return {} My argument is that the intent is clearer in: def get_product_item(jsonld_items): return first((item for item in jsonld_items if item['@type'] == 'Product'), {}) As a reminder, first()'s definition in Python is: def first(seq, default=None): return next(iter(seq), default=default) It could be … [View More]

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Allow user extensions to operators [related to: Moving PEP 584 forward (dict + and += operators)]
by Random832 Dec. 5, 2019

Dec. 5, 2019

What if there was a general mechanism to allow operators to be implemented by user code that does not belong to the class? If the name [e.g.] __operatorhook_or__ is defined anywhere in a module, within that module all calls to that operator are replaced with a two-step process: call __operatorhook_or__(dict1, dict2) if it returns a value, use that value if it returns NotImplemented use the ordinary operator lookup process, i.e. dict1.__or__ and dict2.__ror___ [if __operatorhook_or__ is not … [View More]

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Archiving Threads / Closing Threads
by Abdur-Rahmaan Janhangeer Dec. 5, 2019

Dec. 5, 2019

I suggest we find a way to close a mail thread. Obviously we can't stop people from sending mails, but, like when a mod sees the topic has been juiced out, he closes the topic which practically means: if mailman sees mails being sent to a topic closed by a mod, it does not relay it to the list. It is normally difficult to say when a topic has been juiced out (the essentials have been said, with no new inputs). One might close the topic prematuraly. So, a time-based automatic closing might be … [View More]

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Re: Fwd: re.findfirst()
by Guido van Rossum Dec. 5, 2019

Dec. 5, 2019

Well said! On Wed, Dec 4, 2019 at 16:33 Juancarlo Añez <juancarlo.anez(a)gmail.com> wrote: > > > On Wed, Dec 4, 2019 at 3:02 PM Guido van Rossum <guido(a)python.org> wrote: > >> Fair enough. I’ll let the OP defend his use case. >> > > The OP thinks that the case for wanting just the string for a first regex > match, or a verifiable default if there is no match, is way too common, > that the advice on the web is not very good (it should be "write … [View More]

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Fwd: re.findfirst()
by Juancarlo Añez Dec. 4, 2019

Dec. 4, 2019

There are many ugly recipes about to handle the common use case that could be handled by: def findfirst(regex, text, default=None, flags=0): return next(finditer(regex, text, flags=flags), default=default) The matching and return value semantics would be the same as those of *re.findall()*, but the search would stop on the first match, or return "default" if there wasn't a match (*findfirst()* will return a tuple when more than one group is matched). Typically programmers will use: … [View More]

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math.copysign not to introduce float
by Marein Dec. 4, 2019

Dec. 4, 2019

The math.copysign(x, y) function always returns a float, even when the given x is an int, i.e. math.copysign(3, -1) gives -3.0. This is documented behaviour, but I find it somewhat surprising given that the name suggests that it only copies a sign, and it's also annoying in situations when an int is strictly needed (i.e. as the step argument to range), requiring an additional cast. I'm interested to hear whether it might be a good idea to preserve the int/float type of the argument in math.copysign.

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PEP's shouldn't require a sponsor
by Batuhan Taskaya Dec. 4, 2019

Dec. 4, 2019

Why do i need to convince a core developer for my PEP? AFAIK the steering council can include non core developers (i know it isn't that current case but for the future this is important). And if the last authority who will approve my PEP is the steering council i just need to convince them not core developers. Sponsors can stay (and they should because guidance is important) but thy shouldn't be mandatory. Let everyone to send their peps.

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namedtuple for dict.items()/collections.abc.Mappings.items()
by Soni L. Dec. 1, 2019

Dec. 1, 2019

I have a lot of code that looks like this: def filter(self, it, defs): for x in it: for y in _match_helper(self.key, defs, x[0]): yield (y, x[1]) def filter(self, it): for el in it: &… [View More]

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Access to member name/names via context during Enum instance initialization
by Steve Jorgensen Dec. 1, 2019

Dec. 1, 2019

I brought this up before, but I had a kind of weak understanding of `enum.Enum` at the time, so my expression of the issue and proposal for a solution were pretty awkward. Basically, with the current implementation of `Enum` and supporting classes, the only way that a member can have access to its own name during or prior to its initialization is if/when its value is auto-generated, so if you want to specify a value rather than having it auto-generated (e.g. to generate a label attribute) then … [View More]

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