What are type guards in MyPy?

What are type guards in MyPy?

Type guards in MyPy are special functions that help narrow down the type of a variable within a specific scope.

Can you give me an example of how to use a type guard?

Sure! Here's a simple example:

from typing import Union, TypeGuard

def is_str_list(val: Union[list, str]) -> TypeGuard[list[str]]:
    return all(isinstance(i, str) for i in val)

my_var: Union[list, str] = ['hello', 'world']
if is_str_list(my_var):
    print('This is a list of strings!')

What happens if the type guard fails?

If the type guard fails, MyPy will treat the variable as its original type, and you may encounter type errors if you try to use it as a narrowed type.

Are there any limitations to using type guards?

Yes, type guards can only be used with certain types of checks and may not cover all scenarios, especially with complex types.