examples/functions/duplicate_add_from_module.py
from __future__ import print_function

from mycalc import add
print(add(2, 3))  # 5

from mymath import add
print(add(2, 3))  # 6


from mycalc import add
print(add(2, 3))  # 5

The second declaration silently overrides the first declaration.

pylint can find such problems, along with a bunch of others.