Make several argument defaults immutable (and annotate them) #17496
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Mutable function argument defaults can be modified persistently (see Ruff rule B006). In several functions mutable default empty sets or lists can easily be replaced with immutable empty tuples, which makes it obvious that these defaults are not modified.
eerovaher
added
units
no-changelog-entry-needed
typing
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mhvk
reviewed
Dec 3, 2024
| @@ -2262,13 +2262,34 @@ class CompositeUnit(UnitBase): | |||
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| _decomposed_cache: CompositeUnit | None = None | |||
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| @overload | |||
There was a problem hiding this comment.
Maybe add a comment along the lines of
# The typing overloads here refect that with `_error_check=False`,
# we can count on the scale and power being sanitized already.
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p.s. Just to be clear, I'm fine with the change to empty tuples; it works fine here. |
nstarman
reviewed
Dec 3, 2024
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Description
The first commit adds annotations to a few functions in
units, all of which have a parameter with the typeCollection[UnitBase]1. In several functions with such a parameter its default value is an emptysetor an emptylist, both of which are mutable. In Python it is possible to permanently modify mutable function parameter defaults, which can cause bugs (see also Ruff rule B006 (mutable-argument-default)). It is better to use an immutable default such as an emptytuplebecause then it is obvious just from reading the function signature that calling the function does not modify the default argument.Usually I prefer to avoid changing code in type annotation pull requests, but in this case the annotations make it obvious that the sets and lists can be replaced with tuples without changing code behavior, so adding the annotations and changing the code are conceptually related.
Footnotes
I find it somewhat difficult to understand why the type is
Collection[UnitBase]instead ofCollection[NamedUnit], but there is a test that asserts thatNamedUnitis too restrictive: https://github.com/astropy/astropy/blob/24d3dd96015839ecf87899b02d403a9002bd3ef6/astropy/units/tests/test_units.py#L749-L755 ↩