gistfile1.py

def user_validator(obj):
    return True

class BaseHandler(object):
    validator = None

    def post(self, data):
        if self.validator(data):
            return 'ok'
        else:
            return 'error'


class UserHandler(BaseHandler):
    validator = user_validator


def main():
    user_handler = UserHandler()
    print user_handler.post('somedata')


if __name__ == '__main__':
    main()

gistfile2.pytb

Traceback (most recent call last):
  File "/Users/t0ster/Desktop/test.py", line 24, in <module>
    main()
  File "/Users/t0ster/Desktop/test.py", line 20, in main
    print user_handler.post('somedata')
  File "/Users/t0ster/Desktop/test.py", line 8, in post
    if self.validator(data):
TypeError: user_validator() takes exactly 1 argument (2 given)
[Finished in 0.1s with exit code 1]