from unittest.mock import patch


SOME_LIST = [1, 2]


def ludicrous_len(l):
    return 7777


patch_len = patch('__main__.len', ludicrous_len)


@patch_len
def example_return_decorated():
    return len(SOME_LIST)


@patch_len
def example_yield_decorated():
    yield len(SOME_LIST)


out1 = example_return_decorated()
out2 = list(example_yield_decorated())

print()
print(out1)  # We get 7777, patch has worked.
print(out2)  # We get [2], patch has not been applied.
print()


assert out1 == 7777
assert out2 == [2]