custom sorting and __cmp__

Aahz aahz at pythoncraft.com
Wed Dec 3 03:10:19 CET 2003


In article <slrnbsk5ms.1pe.missive at homer.easthighschool.net>,
Lee Harr  <missive at hotmail.com> wrote:
>
>>>> a1 == c
>Traceback (most recent call last):
>  File "<stdin>", line 1, in ?
>  File "<stdin>", line 5, in __cmp__
>AttributeError: C instance has no attribute 'level'
>
>Should I be catching comparisons to objects that do not have
>my 'level' attribute and falling back to id comparison?
>Or am I worried about nothing (YAGNI :o) ?

Python is these days moving more and more toward preventing
heterogeneous comparisons:

>>> import datetime, time
>>> d=datetime.date.fromtimestamp(time.time())
>>> d>1
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: can't compare datetime.date to int

However, you should set things up so that you can use ``==``:

>>> d==1
False

The easy way to handle this is to use the new special methods for rich
comparisons instead of __cmp__.
-- 
Aahz (aahz at pythoncraft.com)           <*>         http://www.pythoncraft.com/

Weinberg's Second Law: If builders built buildings the way programmers wrote 
programs, then the first woodpecker that came along would destroy civilization.




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