def add(x: int, y: int) -> int:
    return x+y

This is valid Python 3 code!

def square(x):
    """Computes square of a number."""
    return x*x

>>> square.__name__
'square'
>>> square.__module__
'__main__'
>>> square.__doc__
'Computes square of a number.'

• It is a static type checker for Python
• Written by Jukka for his Ph.D. thesis.

• PEP 3107 - Function Annotations
• [Python-ideas] Proposal: Use mypy syntax for function annotations - Guido

Anand Chitipothu http://anandology.com/ @anandology

Slides: http://anandology.com/presentations/python3-function-anotations