How to use Python filter()

By Flavio Copes

Learn how to use the Python filter() function to keep only the items of an iterable that pass a test, using a named function or a concise lambda function.

Python provides 3 useful global functions we can use to work with collections: map(), filter() and reduce().

Tip: sometimes list comprehensions make more sense and are generally considered more pythonic

filter() takes an iterable and returns a filter object, which is another iterable, but without some of the original items.

You do so by returning True or False from the filtering function:

numbers = [1, 2, 3]

def isEven(n):
    return n % 2 == 0

result = filter(isEven, numbers)

print(list(result)) # [2]

You can use a lambda function to make the code more concise:

numbers = [1, 2, 3]

result = filter(lambda n: n % 2 == 0, numbers)

print(list(result)) # [2]

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