Question

The problem: I have a class which contains a template method execute which calls another method _execute. Subclasses are supposed to overwrite _execute to implement some specific functionality. This functionality should be documented in the docstring of _execute. Advanced users can create their own subclasses to extend the library. However, another user dealing with such a subclass should only use execute, so he won’t see the correct docstring if he uses help(execute).

Therefore it would be nice to modify the base class in such a way that in a subclass the docstring of execute is automatically replaced with that of _execute. Any ideas how this might be done?

I was thinking of metaclasses to do this, to make this completely transparent to the user.

Answer 1

Well, if you don’t mind copying the original method in the subclass, you can use the following technique.

import new  def copyfunc(func):     return new.function(func.func_code, func.func_globals, func.func_name,                         func.func_defaults, func.func_closure)  class Metaclass(type):     def __new__(meta, name, bases, attrs):         for key in attrs.keys():             if key[0] == '_':                 skey = key[1:]                 for base in bases:                     original = getattr(base, skey, None)                     if original is not None:                         copy = copyfunc(original)                         copy.__doc__ = attrs[key].__doc__                         attrs[skey] = copy                         break         return type.__new__(meta, name, bases, attrs)  class Class(object):     __metaclass__ = Metaclass     def execute(self):         '''original doc-string'''         return self._execute()  class Subclass(Class):     def _execute(self):         '''sub-class doc-string'''         pass