recursion in __cmp__

Peter Otten __peter__ at web.de
Fri Nov 5 10:55:12 CET 2004


Victor Safronovich wrote:

> please comment this
> Python 2.2.3 (#42, May 30 2003, 18:12:08) [MSC 32 bit (Intel)] on win32
>>>> class A:
> def __cmp__(self, other):
> print '%s|%s' %(`self`, `other`)
> return cmp(self, other)
> 
>>>> a = A()
>>>> cmp(a,A())
 
Does it get clearer with the following reimplementation of cmp()?

>>> class A:
...     def __cmp__(self, other):
...             return mycompare(self, other)
...
>>> def mycompare(a, b):
...     try:
...             return a.__cmp__(b)
...     except AttributeError:
...             return mycompare(id(a), id(b))
...
>>> mycompare(A(), A())
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "<stdin>", line 3, in mycompare
  File "<stdin>", line 3, in __cmp__
  File "<stdin>", line 3, in mycompare
  File "<stdin>", line 3, in __cmp__
  [snip]
  File "<stdin>", line 3, in __cmp__
  File "<stdin>", line 3, in mycompare
RuntimeError: maximum recursion depth exceeded
>>>

Peter




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