[Python-Dev] Updated Monkey Typing pre-PEP

[Raymond Hettinger]

[Guido van Rossum]
> There's one other problem that Phillip tries to tackle in his
> proposal: how to implement the "rich" version of an interface if all
> you've got is a partial implementation (e.g. you might have readline()
> but you need readlines()). I think this problem is worthy of a
> solution, but I think the solution could be found, again, in a
> traditional adapter class. Here's a sketch::
> 
> class RichFile:
>     def __init__(self, ref):
>         self.__ref = ref
>         if not hasattr(ref, 'readlines'):
>             self.readlines = self.__readlines # Other forms of this
> magic are conceivably
>     def __readlines(self): # Ignoring the rarely used optional
argument
>         # It's tempting to use [line for line in self.__ref] here but
> that doesn't use readline()
>         lines = []
>         while True:
>             line = self.__ref.readline()
>             if not line:
>                 break
>             lines.append(line)
>         return lines
>     def __getattr__(self, name): # Delegate all other attributes to
> the underlying object
>         return getattr(self.__ref, name)

Instead of a __getattr__ solution, I recommend subclassing from a mixin:

    class RichMap(SomePartialMapping, UserDict.DictMixin): pass

    class RichFile(SomePartialFileClass, Mixins.FileMixin): pass



Raymond