On Tue, Apr 6, 2010 at 2:11 PM, Gustavo Narea <m...@gustavonarea.net> wrote: > Hello! > > Could you please confirm whether my understanding of equality > operations in sets and lists is correct? This is how I think things > work, partially based on experimentation and the online documentation > for Python: > > When you compare two lists, *every* element of one of the lists is > compared against the element at the same position in the other list; > that comparison is done by the __eq__() method (or the equivalent for > builtin types). This is interrupted when a result is False. > > When you compare two sets, there's a loop over all the elements of the > first set, where the hash for that element is looked up in the second > set: [snip] > In other words: The more different elements two collections have, the > faster it is to compare them as sets. And as a consequence, the more > equivalent elements two collections have, the faster it is to compare > them as lists. > > Is this correct?
Yes, but faster isn't the same thing as free. I still get bitten occasionally by code that blows away the difference by including a set-wise assert() in a loop. Also, lists can have mutable members so there are times you really /do/ want to compare lists instead of hashes. -Jack -- http://mail.python.org/mailman/listinfo/python-list
