cmp of multiple attributes

[Alex Martelli]

Roy Smith <roy at panix.com> wrote:

> >Roy Smith wrote:
> >>     def __cmp__ (self, other):
> >>    # I wish there was a less verbose way to do this!
> >>         if self.block < other.block:
> >>             return -1
> >>         if self.block > other.block:
> >>             return 1
> >>         if self.lot < other.lot:
> >>             return -1
> >>         if self.lot > other.lot:
> >>             return 1
> >>         return 0
> 
> Steven Bethard  <steven.bethard at gmail.com> wrote:
> >Does this do what you want?
> >...     def __cmp__(self, other):
> >...         return (cmp(self.block, other.block) or
> >...                 cmp(self.lot, other.lot))
> 
> Yes, that's exactly what I was after.  Like so many things, it's
> obvious once it's pointed out to you.  Thanks!

Better still, IMHO:

def __cmp__(self, other):
    return cmp((self.block,self.lot), (other.block,other.lot))

Comparisons of tuples, lists, etc, are *lexicographical*: the first
items are compared; iff they're equal, then the second items, and so
forth.  IOW, exactly what you want in this case.


Alex