Mailman 3 January 2023 - Python-ideas

PEP 671 (late-bound arg defaults), next round of discussion!
by Chris Angelico 23 Jul '23

23 Jul '23

I've just updated PEP 671 https://www.python.org/dev/peps/pep-0671/ with some additional information about the reference implementation, and some clarifications elsewhere. *PEP 671: Syntax for late-bound function argument defaults* Questions, for you all: 1) If this feature existed in Python 3.11 exactly as described, would you use it? 2) Independently: Is the syntactic distinction between "=" and "=>" a cognitive burden? (It's absolutely valid to say "yes" and "yes", and feel free to say which of those pulls is the stronger one.) 3) If "yes" to question 1, would you use it for any/all of (a) mutable defaults, (b) referencing things that might have changed, (c) referencing other arguments, (d) something else? 4) If "no" to question 1, is there some other spelling or other small change that WOULD mean you would use it? (Some examples in the PEP.) 5) Do you know how to compile CPython from source, and would you be willing to try this out? Please? :) I'd love to hear, also, from anyone's friends/family who know a bit of Python but haven't been involved in this discussion. If late-bound defaults "just make sense" to people, that would be highly informative. Any and all comments welcomed. I mean, this is python-ideas after all... bikeshedding is what we do best! The reference implementation currently has some test failures, which I'm looking into. I'm probably going to make this my personal default Python interpreter for a while, to see how things go. ChrisA

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Re: Multiple arguments to str.partition and bytes.partition
by Peter Ludemann 10 Jan '23

10 Jan '23

You can get almost the same result using pattern matching. For example, your "foo:bar;baz".partition(":", ";") can be done by a well-known matching idiom: re.match(r'([^:]*):([^;]*);(.*)', 'foo:bar;baz').groups()

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Multiple arguments to str.partition and bytes.partition
by James Addison 10 Jan '23

10 Jan '23

Hi folks, I'd like to gather some feedback on a feature suggestion to extend str.partition and bytes.partition to support multiple arguments. Please find the feature described below. # Feature or enhancement The str.partition[1] method -- and similarly the bytes.partition[2] method -- is useful when dividing an input into subcomponents while returning a tuple of deterministic length (currently 3) and potentially retaining the delimiters. The feature described here adds support for multiple positional arguments to those methods. The first positional argument would be applied to the input instance that the method is called from -- no change from existing behaviour. Subsequent positional arguments would be applied to the rightmost component of the previous application of the partition algorithm. So, for example, in pseudocode: ### Single-argument case (matching existing behaviour) >>> "foo:bar".partition(":") >>> # partition 'foo:bar' using ':' >>> - result = ['foo', ':', 'bar'] >>> # all positional arguments consumed >>> - return result ### Multiple-argument case (added feature) >>> "foo:bar;baz".partition(":", ";") >>> # partition 'foo:bar;baz' using ':' >>> - result = ['foo', ':', 'bar;baz'] >>> # positional arguments remain; continue >>> # partition 'bar;baz' using ';' >>> - result = ['foo', ':', 'bar', ';', 'baz'] >>> # all positional arguments consumed >>> - return result # Pitch Multiple-partition-arguments would provide a shorthand / syntactic sugar to abbreviate the process of separating inputs with known-delimeters into components. For example: >>> login_string = 'username@hostname:2001' >>> username, _, hostname, _, port = login_string.partition('@', ':') Beneficially for the caller, the number of tuple elements can be determined based on the number of positional arguments. For n arguments, a tuple of length 2n + 1 will be returned. Thank you for any and all feedback. James [1] - https://docs.python.org/3/library/stdtypes.html#str.partition [2] - https://docs.python.org/3/library/stdtypes.html#bytes.partition

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