What can MyPy detect and what can it not?

Question

I just started with MyPy to add more static typing to my python programs. I tried this:

import sys

def summe (a: int, b: int):
    print (a + b)    

def main():       
    x: int = 10  
    y: int = 20
    z: str = '30'
    summe (x, y) 
    summe (x, z) 


if __name__ == '__main__':
    sys.exit(main()) 

and this is obviously a type error and crashes at runtime but MyPy says: Success: no issues found in 1 source file

Am I doing something wrong, missed some setting? I have Windows 10, Python 3.10, latest MyPy under Eclipse.

Answer 1

Your main is not being type-checked as you have not annotated it. Add the annotation:

def main() -> None:

And the second summe call will cause a type error as you expect.