filter() in python

The filter() method filters the given sequence with the help of a function that tests each element in the sequence to be true or not.

syntax:

filter(function, sequence)
Parameters:
function: function that tests if each element of a 
sequence true or not.
sequence: sequence which needs to be filtered, it can 
be sets, lists, tuples, or containers of any iterators.
Returns:
returns an iterator that is already filtered.

# function that filters vowels
def fun(variable):
    letters = ['a', 'e', 'i', 'o', 'u']
    if (variable in letters):
        return True
    else:
        return False


# sequence
sequence = ['g', 'e', 'e', 'j', 'k', 's', 'p', 'r']

# using filter function
filtered = filter(fun, sequence)

print('The filtered letters are:')
for s in filtered:
    print(s)

Output:

The filtered letters are:
e
e

Application:
It is normally used with Lambda functions to separate list, tuple, or sets.

# a list contains both even and odd numbers.
seq = [0, 1, 2, 3, 5, 8, 13]

# result contains odd numbers of the list
result = filter(lambda x: x % 2 != 0, seq)
print(list(result))

# result contains even numbers of the list
result = filter(lambda x: x % 2 == 0, seq)
print(list(result))

Output:

[1, 3, 5, 13]
[0, 2, 8]

Please refer Python Lambda functions for more details.