Python filter()

Python filter() builtin function is used to filter elements of an iterable based on a function. Elements of the iterable for which the return value of function is True, make it to the result.

In this tutorial, we will learn about the syntax of Python filter() function, and learn how to use this function with the help of examples.

Syntax

The syntax of filter() function is

filter(function, iterable)

where

ParameterRequired/OptionalDescription
functionRequiredPython function that filters the given iterable.
iterableRequiredIterable to be filtered.

Returns

The function returns a filter object. We can typecast it to required collection type.

Examples

Filter Even Numbers from List

In this example, we take a list of integers and filter only even values in it.

Python Program

def even(x):
    return x % 2 == 0

a = [2, 5, 7, 8, 10, 13, 16]

result = filter(even, a)
print('Original List :', a)
print('Filtered List :', list(result))
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Output

Original List : [2, 5, 7, 8, 10, 13, 16]
Filtered List : [2, 8, 10, 16]

Filter with Lambda Function

We can also provide a lambda function for function parameter of filter().

Python Program

a = [2, 5, 7, 8, 10, 13, 16]
result = filter(lambda x: x % 2 == 0, a)
print('Original List :', a)
print('Filtered List :', list(result))
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Output

Original List : [2, 5, 7, 8, 10, 13, 16]
Filtered List : [2, 8, 10, 16]

Remove Vowels from String

In this example, we take a string and remove vowels from string by filtering only those characters that are not vowels.

Python Program

a = 'Hello World'
result = filter(lambda x: x.lower() not in ['a', 'e', 'i', 'o', 'u'], a)
result = ''.join(list(result))
print('Original List :', a)
print('Filtered List :', result)
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Output

Original List : Hello World
Filtered List : Hll Wrld

Conclusion

In this Python Tutorial, we have learnt the syntax of Python filter() builtin function, and also learned how to use this function, with the help of Python example programs.