Python filter() function

The filter() method facilitates a functional approach to Python programming . It allows the developer to write simpler, shorter code , without necessarily needing to bother about intricacies like loops and branching.

The filter() method returns an iterator were the items are filtered through a function to test if the item is accepted or not. The returned iterable may be either a sequence, a container which supports iteration, or an iterator. If function is None , the identity function is assumed, that is, all elements of iterable that are false are removed.

Syntax

 
filter(function, iterable)

function : The function that tests if elements of an iterable returns true or false.
iterable : The iterable to be filtered.

How to filter a list in Python

 
# The function that tests if elements of an iterable returns true or false
def foo(var):
    directions = ['east', 'west', 'north', 'south']
    if (var in directions):
        return True
    else:
        return False
# The list to be filtered
myList = ['sunday', 'east', 'march', 'west', '101', 'north', 'abcd', 'south']
# using filter function
filtered = filter(foo, myList)
print('Filtered directions are:')
for str in filtered:
    print(str)

output

 
Filtered directions are:
east
west
north
south

How to use the filter() method in Python

Python filter using lambda expression

 
myList = [10, 15, 40, 6, 30, -20]
# Returns the elements which are multiples of 10
filtered = list(filter(lambda n : n%10 == 0, myList))
print(filtered)

output

 
[10, 40, 30, -20]

Next : Difference between range() and xrange() in Python