Mailman 3 August 2023 - Python-Dev

Proposal: Allow non-default after default arguments
by Sebastian Rittau Oct. 16, 2023

Oct. 16, 2023

Currently, Python doesn't allow non-default arguments after default arguments: >>> def foo(x=None, y): pass File "<stdin>", line 1 def foo(x=None, y): pass ^ SyntaxError: non-default argument follows default argument I believe that at the time this was introduced, no use cases for this were known and this is is supposed to … [View More]prevent a source of bugs. I have two use cases for this, one fringe, but valid, the other more important: The fringe use case: Suppose you have a function that takes a 2D coordinate value as separate "x" and "y" arguments. The "x" argument is optional, the "y" argument isn't. Currently there are two ways to do this, none of them particularly great: def foo(y, x): # reverse x and y arguments, confusing ... def foo(x, y=None): # Treat the x argument as y if only one argument is provided if y is None: x, y = y, x ... To me, the "natural" solution looks like this: def foo(x=None, y): ... # Called like this: foo(1, 2) foo(y=2) This could also be useful when evolving APIs. For example there is a function "bar" that takes two required arguments. In a later version, the first argument gains a useful default, the second doesn't. There is no sensible way to evolve the API at the moment. The more important use case involves @overloads. A condensed example of a function where the return type depends on an "encoding" parameter, followed by further parameters that could be called like this: foo(123, "utf-8") # would return bytes foo(encoding="utf-8") foo(123, None) # would return str foo(encoding=None) foo(x=123) # would return str foo() This could ideally be written as: @overload def foo(x: int = ..., encoding: None = ...) -> str: ... @overload def foo(x: int = ..., encoding: str) -> bytes: ... # plus the actual implementation But due to the syntax constraint, this needs to be hacked around with a third overload: @overload def foo(x: int = ... encoding: None = ...) -> str: ... @overload def foo(x: int, encoding: str) -> bytes: ... # for foo(123, "utf-8") @overload def foo(*, encoding: str) -> bytes: ... # for foo(encoding="utf-8") Not only is this hard to read, real examples in typeshed are usually more complex, with many arguments before or after the affected argument or even multiple affected arguments. This often becomes too complex to write or maintain. Here is one example from the wild: https://github.com/python/typeshed/blob/b95b729b9e07ab21d252701af0f5b740467… Allowing non-default arguments after default arguments would solve both use cases above and eliminates a special case. I'm also not sure what exactly the current SyntaxError really protects us from. Adding a non-default after a default argument can't really lead bugs. - Sebastian [View Less]

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[RELEASE] Python 3.11.5, 3.10.13, 3.9.18, and 3.8.18 is now available
by Łukasz Langa Aug. 24, 2023

Aug. 24, 2023

There’s security content in the releases, let’s dive right in. gh-108310 <https://github.com/python/cpython/issues/108310>: Fixed an issue where instances of ssl.SSLSocket <https://docs.python.org/release/3.10.13/library/ssl.html#ssl.SSLSocket> were vulnerable to a bypass of the TLS handshake and included protections (like certificate verification) and treating sent unencrypted data as if it were post-handshake TLS encrypted data. Security issue reported as CVE-2023-40217 1 &… [View More]

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[RELEASE] Python 3.12.0 release candidate 1 released
by Thomas Wouters Aug. 6, 2023

Aug. 6, 2023

I'm pleased to announce the release of Python 3.12.0rc1: https://www.python.org/downloads/release/python-3120rc1/ This is the first release candidate of Python 3.12.0 This release, *3.12.0rc1*, is the penultimate release preview. Entering the release candidate phase, only reviewed code changes which are clear bug fixes are allowed between this release candidate and the final release. The second candidate (and the last planned release preview) is scheduled for Monday, 2023-09-04, while the … [View More]

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Some pattern annoyance
by Christian Tismer-Sperling Aug. 3, 2023

Aug. 3, 2023

Hi folks, I just used Structural Pattern Matching quite intensively and I'm pretty amazed of the new possibilities. But see this code, trying to implement Mark Pilgrim's regex algorithm for roman literals with SPM: With constants, I can write match seq: case "M", "M", "M", "M", *r: return 4 * 1000, r But if I want to use abbreviations by assignment, this is no longer possible, and I have to write something weird like: M = "M" match seq: case a,… [View More]

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