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Enable Final instance attributes for attrs #14232

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merged 2 commits into from
Dec 6, 2022

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Tinche
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@Tinche Tinche commented Dec 1, 2022

A quick patch to enable the following scenario:

@define
class C:
    a: Final[int]  # `a` is a final instance attribute

There are some edge cases I haven't covered here that would be complex to handle and not add much value IMO, so I think this will be useful like this.

For example:

@define
class C:
    a: Final[int] = field(init=False)

This is technically not sound, but there might be an __attrs_post_init__ on the class or one of its ancestors and that function might set it.

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if attribute.name in ti.names:
sym_node = ti.names[attribute.name].node
if isinstance(sym_node, Var) and sym_node.is_final:
sym_node.final_set_in_init = True
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This seems to potentially modify the symbol node of a base class. That is not safe to do, since we may have serialized an earlier version of the class, etc. So probably best to do this only for attributes defined in the current class?

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@JukkaL Good catch, fix applied.

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github-actions bot commented Dec 6, 2022

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

@JukkaL JukkaL merged commit 7e9aa74 into python:master Dec 6, 2022
@Tinche Tinche deleted the attrs/final-instance-attributes branch December 6, 2022 17:00
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2 participants