Iterating across a filtered list
bdesth.quelquechose at free.quelquepart.fr
Tue Mar 13 21:53:22 CET 2007
Paul Rubin a écrit :
> "Drew" <olsonas at gmail.com> writes:
>>You're exactly on the mark. I guess I was just wondering if your first
>>example (that is, breaking the if statement away from the iteration)
>>was preferred rather than initially filtering and then iterating.
> I think the multiple statement version is more in Python tradition.
I don't know if I qualify as a Python traditionalist, but I'm using
Python since the 1.5.2 days, and I usually favor list comps or generator
expressions over old-style loops when it comes to this kind of operations.
> Python is historically an imperative, procedural language with some OO
Python has had functions as first class objects and (quite-limited-but)
anonymous functions, map(), filter() and reduce() as builtin funcs at
least since 1.5.2 (quite some years ago).
> Iterators like that are a new Python feature
List comps are not that new (2.0 or 2.1 ?):
print "\n".join([contact for name, contact in contacts.items() \
> and they have
> some annoying characteristics, like the way they mutate when you touch
While sequences are iterables, all iterables are not sequences. Know
what you use, and you'll be fine.
> It's usually safest to create and consume them in the same
> place, e.g. creating some sequence and passing it through map, filter, etc.
Safest ? Why so ?
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