[Tutor] class wrapper question (from Dive into Python)

[John Abbe]

I'm going through <http://www.diveintopython.org/>, and highly 
recommend it to all the other newbies out there. I'm halfway through 
chapter 3 before a serious question occurred to me. This, like not 
noticing the technology in computer animation movies, is a good thing.

Okay...

 From <http://www.diveintopython.org/fileinfo_specialmethods.html>, 
the old UserDict class:

>     def clear(self): self.data.clear()          1
>     def copy(self):                             2
>         if self.__class__ is UserDict:          3
>             return UserDict(self.data)        
>         import copy                             4
>         return copy.copy(self)                
>     def keys(self): return self.data.keys()     5
>     def items(self): return self.data.items()
>     def values(self): return self.data.values()

My question is, in copy, why bother with checking if it's a 
UserDict...why isn't it just like this?

    def copy(self):
       import copy
       return copy.copy(self)

Life,
John
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