filter() in python - GeeksforGeeks

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.

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