What does ~<type> do?

user_12469275 0
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When writing code I have encountered my linter expressing the type of ~<type> (where <type> is a type not <type> literary). An example of this is self.

class A:
    def foo(self):
        reveal_type(self) # reveals "~A"

I assume this means "A or a subclass of A"; however, I was unable to find any information about it online.

Also, you can't use this syntax in code:

a: ~A # raises an exception: TypeError: bad operand type for unary ~: 'type'

If a would have been revealed it would be Unknown.

python-typing mypy type-hinting python
2 Answers

Looking at the source code, TypeVars are printed (repr) with a leading "+" if they are covariant, "-" if contravariant, and "~" if invariant (neither covariant nor contravariant).

user_73612010

I can't find it in the Mypy documentation, but Pyright seems similar, and its documentation says:

Within the function, the type of self is printed with a tilde preceding the class name. This indicates that the type is a TypeVar bound to the class rather than the class itself.

So I think Mypy's use of ~Classname is the same.

user_14918950
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