How to perform type checking with the typing Python module?

Question

I am reading the typing module code and also looking into mypy to understand how it does type checking. Unfortunately for me, mypy builds a very smart tree with

Answer 1

The library Pyadaaah offers automatic runtime (resp. dynamic) type and range checking as well as signals for class attributes.

E.g. have a look at the belonging youtube video (series) starting with this: https://www.youtube.com/watch?v=Y3Hmg_HQtsY

Which, by the way, also is a quite nice introduction to the (underlying) property/getter/setter mechanism as well.

Pyadaaah does not use the typing library though.

Answer 2

You can easily get the very limited functionality that works correctly for the simple examples provided in your question:

import mypy.api

def check_type(value, typ):
    program_text = 'from typing import *; v: {} = {}'.format(typ, repr(value))
    normal_report, error_report, exit_code = mypy.api.run(['-c', program_text])
    return exit_code == 0

int_ = 1
str_ = 'a'
list_str_ = ['a']
list_int_ = [1]
tuple_int_ = (1,)

assert check_type(int_, 'int')
assert not check_type(str_, 'int')
assert check_type(list_int_, 'List[int]')
assert not check_type(list_str_, 'List[int]')
assert check_type(list_int_, 'List[Any]')
assert check_type(tuple_int_, 'Tuple[int]')

You can even do some more advanced stuff (for example, refer to the types that correspond to classes you defined in your program) by extending this code a bit, so that mypy gets to parse your entire source code as opposed to just the current line.

Alternatively, you might want to look at enforce or typeguard.