I have two functions: def get_foo(params) -> Optional[str] def bar(foo: str) And a function which chains these functions together: def f(params): # other stuff up here foo = get_foo(params) return bar(foo) I know based on the other things happening in my function that the result of get_foo will never be None. When I run mypy against this file, I of course get errors: error: Argument 1 of "bar" has incompatible type "Optional[str]"; expected "str" which makes sense. I could add an assert foo is not None statement, but this is hot-path code and in my tests it has measurable performance impact. I would like to make a type assertion for mypy only. How do I do that? EDIT: I also tried adding a comment #type: str after the assignment statement, but this generated a similar error Continue reading...
