Python 3 reference · Built-in Functions

Python filter() Function

Keep only the items of an iterable for which a function returns True. Returns a lazy iterator, not a list.

Syntax

filter(function, iterable)

Parameter	Description
`function`	Called with each item; keep the item if the result is truthy. `None` keeps truthy items.
`iterable`	The items to filter.

An iterator over the kept items.

Keep matching itemsTry it yourself

numbers = [5, 12, 7, 20, 3]
print(list(filter(lambda n: n > 6, numbers)))

Output

[12, 7, 20]

Remove falsy valuesTry it yourself

print(list(filter(None, ["a", "", None, "b", 0])))

Output

['a', 'b']

The list comprehension equivalentTry it yourself

numbers = [5, 12, 7, 20, 3]
print([n for n in numbers if n > 6])  # usually clearer

Output

[12, 7, 20]

filter() returns an iterator: wrap it in list() to see the items, and remember it can only be used once.
A list comprehension [x for x in items if cond] is often more readable, especially when you also transform the items.

Version	Change
Python 3.0	Added

map() · Apply a function to every item of one or more iterables and return a lazy iterator of the results.
sorted() · Return a new sorted list from any iterable. Supports a key function and reverse order; the original is left unchanged.
any() · Return True if at least one item in an iterable is truthy. Returns False for an empty iterable and stops at the first truthy item.
all() · Return True if every item in an iterable is truthy, or if the iterable is empty. Stops at the first falsy item.
Python List Methods and Comprehensions · tutorial
Python Lambda · tutorial