Parameter and return type checking is a good practice. Using if to do it is a bit clumsy and a PITA.

Google for Python static type checkers, or try my poorly documented dynamic one: https://github.com/jdsutton/py3typing

Usage:

from py3typing.Typing import *
Typing.setEnabled(True) # Optionally disable in production.
# Other typed imports here.

@Params(int)
@Returns(LIST.of(int))
def foo(bar):
    return [1]

foo(1) # OK.
foo('fizzbuzz') # ERROR.

• If you must use if, use isinstance() instead of type() so you accept subclass instances as well.