CODEWITHSUNDEEP
pythonfilter
gwenzek
gwenzek

Reputation: 2944

Python: a more concise way to filter a list

I'd like to execute some code for every element in a list that match some property. So my code would look like:

for x in filter(f, lx):
    do some stuff

But my function f is defined in the object x, so I have to write:

for x in filter(lambda x: x.f(), lx):
    do some stuff

Maybe I'm a bit picky, but I find it stupid to define a lambda function when I already define this function somewhere else... Is there a more efficient and concise way to do what I want ?

Upvotes: 0

Views: 82

Answers (2)

Holt
Holt

Reputation: 37606

Use directly the f method defined in your class:

for x in filter(X.f, lx):
    # do some stuff

A more efficient way using the itertools module to avoid the creation of a new list and use beautiful python generator:

import itertools
for x in itertools.ifilter(X.f, lx):
    # do some stuff

Assumning X is the class of element in lx.

Small example:

class A:
    def __init__ (self, b):
        self.b
    def check (self):
        return self.b < 10

l = [A(8), A(40), A(5), A(7), A(33)]
for a in filter(A.check, l):
    print a.b

Upvotes: 3

Ned Batchelder
Ned Batchelder

Reputation: 375504

Perhaps avoid filter:

for x in lx:
    if x.f():
        # do some stuff

It's more lines, but clearer code. If you find yourself doing it often, make a generator:

def filter_f(lx):
    for x in lx:
        if x.f():
            yield x

...

for x in filter_f(lx):
    # do something

(this came out longer than you'd like I suspect, but demonstrates another way to do it.)

Upvotes: 1

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