this post was submitted on 01 Feb 2024
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Python

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I often find myself defining function args with list[SomeClass] type and think "do I really care that it's a list? No, tuple or Generator is fine, too". I then tend to use Iterable[SomeClass] or Collection[SomeClass]. But when it comes to str, I really don't like that solution, because if you have this function:

def foo(bar: Collection[str]) -> None:
    pass

Then calling foo("hello") is fine, too, because "hello" is a collection of strings with length 1, which would not be fine if I just used list[str] in the first place. What would you do in a situation like this?

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[โ€“] [email protected] 1 points 9 months ago (1 children)

Look at the official docs. There is a table part way down stating which methods are available for each. I pick the one closest to how I use it. So if I'm not mutating I'll use Sequence over List to inform the caller I'm treating as immutable and to safe guard myself from mutating it in my implementation via static type analysis.

https://docs.python.org/3/library/collections.abc.html

[โ€“] [email protected] 2 points 9 months ago

str matches most of these contracts, though, requiring additional checks if a str was passed or one of these collections containing strings.