Mailman 3 July 2021 - Python-ideas

zip(x, y, z, strict=True)
by Ram Rachum Dec. 1, 2022

Dec. 1, 2022

Here's something that would have saved me some debugging yesterday: >>> zipped = zip(x, y, z, strict=True) I suggest that `strict=True` would ensure that all the iterables have been exhausted, raising an exception otherwise. This is useful in cases where you're assuming that the iterables all have the same lengths. When your assumption is wrong, you currently just get a shorter result, and it could take you a while to figure out why it's happening. What do you think?

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disallow assignment to unknown ssl.SSLContext attributes
by Thomas Grainger June 10, 2022

June 10, 2022

I was debugging some code that was using TLSv1.2 when I expected it to only support TLSv1.3, I tracked it down to a call to: context.miunimum_version = ssl.TLSVersion.TLSv1_3 it should have been: context.minimum_version = ssl.TLSVersion.TLSv1_3 I'd like invalid attribute assignment to be prevented at runtime

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Bringing the print statement back
by Guido van Rossum March 2, 2022

March 2, 2022

In Python 3.10 we will no longer be burdened by the old parser (though 3rd party tooling needs to catch up). One thing that the PEG parser makes possible in about 20 lines of code is something not entirely different from the old print statement. I have a prototype: Python 3.10.0a0 (heads/print-statement-dirty:5ed19fcc1a, Jun 9 2020, 16:31:17) [Clang 11.0.0 (clang-1100.0.33.8)] on darwin Type "help", "copyright", "credits" or "license" for more information. Cannot read termcap database; using … [View More]dumb terminal settings. >>> print 2+2 4 >>> print "hello world" hello world >>> print "hello", input("Name:") Name:Guido hello Guido >>> print 1, 2, 3, sep=", " 1, 2, 3 >>> But wait, there's more! The same syntax will make it possible to call *any* function: >>> len "abc" 3 >>> Or any method: >>> import sys >>> sys.getrefcount "abc" 24 >>> Really, *any* method: >>> class C: ... def foo(self, arg): print arg ... >>> C().foo 2+2 4 >>> There are downsides too, though. For example, you can't call a method without arguments: >>> print <built-in function print> >>> Worse, the first argument cannot start with a parenthesis or bracket: >>> print (1, 2, 3) 1 2 3 >>> C().foo (1, 2, 3) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: C.foo() takes 2 positional arguments but 4 were given >>> print (2+2), 42 4 (None, 42) >>> C().foo [0] Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: 'method' object is not subscriptable >>> No, it's not April 1st. I am seriously proposing this (but I'll withdraw it if the response is a resounding "boo, hiss"). After all, we currently have a bunch of complexity in the parser just to give a helpful error message to people used to Python 2's print statement: >>> print 1, 2, 3 File "<stdin>", line 1 print 1, 2, 3 ^ SyntaxError: Missing parentheses in call to 'print'. Did you mean print(1, 2, 3)? >>> And IIRC there have been a number of aborted attempts at syntactic hacks to allow people to call functions (like print) without parentheses, although (I think) none of them made it into a PEP. The PEG parser makes this much simpler, because it can simply backtrack -- by placing the grammar rule for this syntax (tentatively called "call statement") last in the list of alternatives for "small statement" we ensure that everything that's a valid expression statement (including print() calls) is still an expression statement with exactly the same meaning, while still allowing parameter-less function calls, without lexical hacks. (There is no code in my prototype that checks for a space after 'print' -- it just checks that there's a name, number or string following a name, which is never legal syntax.) One possible extension I didn't pursue (yet -- dare me!) is to allow parameter-less calls inside other expressions. For example, my prototype does not support things like this: >>> a = (len "abc") File "<stdin>", line 1 a = (len "abc") ^ SyntaxError: invalid syntax >>> I think that strikes a reasonable balance between usability and reduced detection of common errors. I could also dial it back a bit, e.g. maybe it's too much to allow 'C().foo x' and we should only allow dotted names (sufficient to access functions in imported modules and method calls on variables). Or maybe we should only allow simple names (allowing 'len x' but disallowing 'sys.getrefcount x'. Or maybe we should really only bring back print statements. I believe there are some other languages that support a similar grammar (Ruby? R? Raku?) but I haven't investigated. Thoughts? -- --Guido van Rossum (python.org/~guido) *Pronouns: he/him **(why is my pronoun here?)* <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-…> [View Less]

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Adding a thin wrapper class around the functions in stdlib.heapq
by bunslow Feb. 17, 2022

Feb. 17, 2022

Nothing so bombastic this time. The heapq functions are basically all named "heapsomething", and basically all take a "heap" for their first argument, with supplementary args coming after. It's a textbook example of the (hypothetical) Object Oriented Manifesto™ where defining a class increases type safety and programmers' conceptual clarity. There're practically no drawbacks, and the code to be added would be very simple. Updating the tests and docs would probably be harder. In pure Python, … [View More]

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Allow syntax "func(arg=x if condition)"
by Peter O'Connor Jan. 19, 2022

Jan. 19, 2022

I often find that python lacks a nice way to say "only pass an argument under this condition". (See previous python-list email in "Idea: Deferred Default Arguments?") Example 1: Defining a list with conditional elements include_bd = True current_way = ['a'] + (['b'] if include_bd else [])+['c']+(['d'] if include_bd else []) new_way = ['a', 'b' if include_bd, 'c', 'd' if include_bd] also_new_way = list('a', 'b' if include_bd, 'c', 'd' if include_bd) Example 2: Deferring to … [View More]

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Python Documentation in Bengali (translation)
by sharifmehedi24＠outlook.com Sept. 16, 2021

Sept. 16, 2021

Hi there all, I am preparing a team to start translating python documentation to Bengali. I'd appreciate some reference materials, comments and ideas about this. Thank you

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Create a @deprecated decorator (annotation)
by Leonardo Freua Aug. 15, 2021

Aug. 15, 2021

[Migrating from https://bugs.python.org/issue44701] Would it be interesting to create a @deprecated decorator to avoid adding warnings.warn("deprecation message", DeprecationWarning, stacklevel=2) in methods body? Using the decorator approach to indicate depreciation would make the methods cleaner (leaving only their responsibilities in the body) and would be easier to identify, as the cue would be close to the method signature and not mixed with the logic inside the body. in some cases it … [View More]

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copy-paste code snippets to the python console
by Raymond Bisdorff Aug. 15, 2021

Aug. 15, 2021

Dear Python developers, It would be helpful, if the following issue with copy-pasting python code-snippets into the standard shell console, could be investigated and corrected. https://stackoverflow.com/questions/2501208/copying-and-pasting-code-into-t… In particular, copying and pasting from sphinx python and pycon code-blocks with copy button (only >>> and ... lines), is at present not generally working due to the "the shell-s de-indent cmd" need for empty lines. See … [View More]

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More natural type hints for built-in containers
by Ignacio Pickering Aug. 1, 2021

Aug. 1, 2021

Currently type hints for built-in containers are, in my opinion, less succint than required. I suspect it is probably not very difficult for a type checker to interpret something like this for example: var1: {str: (int, int)} = {"label": (1, 2)} var2: {str} = {"other_label"} def function(param1: {int: str} = {1: "foo"}, param2: (int, ...) = (1, 2, 3)) -> (int, (str, ...)): return 3, ("foo", "bar") as equivalent to: var1: dict[str, tuple[int, int]] = {"label": (1, 2)} var2: set[str] = … [View More]

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Possibility to specify port in __init__ of ftplib.FTP
by Marty July 31, 2021

July 31, 2021

Hi. If there is possible to connect and login to ftp server within __init__, I think it would make sense to add parameter **port** in ftplib.FTP. It could look like this: ``` def __init__(self, host='', port=0, user='', passwd='', acct='', timeout=_GLOBAL_DEFAULT_TIMEOUT, source_address=None, *, encoding='utf-8'): self.encoding = encoding self.source_address = source_address self.timeout = timeout if host: self.connect(host, port) … [View More]

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