typing.cast() is ignored
#1885
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Hello, I was trying to use For instance: import typing
a = 1
typing.cast(str, a)
a += "foo"Currently fails with: $ mypy test.py
test.py:5: error: Unsupported operand types for + ("int" and "str") [operator]
Found 1 error in 1 file (checked 1 source file)... which is, in theory, correct, but I was under the assumption that I'm using mypy 1.13.0 with Python 3.12 (it has the same behavior with 3.13) ; I don't have any specific mypy settings configured here. |
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Replies: 1 comment 1 reply
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Hi! This is expected. For example, valid (albeit dubious) uses of a = typing.cast(str, 1)
a += "foo"
# or
a = 1
a += typing.cast(int, "foo")Could you elaborate a bit on what you're trying to achieve? There might be a different typing construct better suited for the task than |
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Oh no, I'm stupid 🤦 Thanks for pointing this out, this is actually super useful 😅
I'm using an external library that has type annotations ... but incorrectly defined. I was trying to force the correct types until the library fixes its type annotations and ships a new version. |
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Hi! This is expected.
castonly changes the type of an expression. It doesn't change the type of variables or otherwise propagate typing assumptions to parts of the program outside of the expression it's used on.For example, valid (albeit dubious) uses of
castmight look likeCould you elaborate a bit on what you're trying to achieve? There might be a different typing construct better suited for the task than
typing.cast.