How do you specify and enforce an interface spec in Python?

An interface specification for a module as provided by languages such as C++ and Java describes the prototypes for the methods and functions of the module. Many feel that compile-time enforcement of interface specifications help in the construction of large programs. Python does not support interface specifications directly, but many of their advantages can be obtained by an appropriate test discipline for components, which can often be very easily accomplished in Python. There is also a tool, PyChecker, which can be used to find problems due to subclassing.

A good test suite for a module can at once provide a regression test and serve as both a module interface specification and a set of examples. Many Python modules can be run as a script to provide a simple “self test.” Even modules which use complex external interfaces can often be tested in isolation using trivial “stub” emulations of the external interface. The doctest and unittest modules or third-party test frameworks can be used to co