human
Here's a good function header given the following:
I wrote the below code

    class Implementation(interface, ):
        def __init__(self, value):
            self.value = value
        def add(self):
            interface.counter += self.value
        def subtract(self):
            interface.counter -= self.value
    return Implementation

What's a good function header?
assistant
#Here's a good function header.

@pytest.fixture()
def implementation(interface):