Python Built-in Functions: map, filter, zip

Python Built-in Functions: map, filter, zip

Map

Make an iterator that computes the function using arguments from each of the iterables. Stops when the shortest iterable is exhausted.

def square(num):
    return num ** 2

numbers = [1,2,3,4,5]
squares=[]
for i in numbers:
    squares.append(square(i))

print(squares)

squares_with_map=map(square,numbers)

print(list(squares_with_map))

Filter

Return an iterator yielding those items of iterable for which function(item) is true. If function is None, return the items that are true.

def even(num):
    if (num % 2) == 0:
        return True
    return False

numbers = [1,2,3,4,5]
even_numbers = []
for i in numbers:
    if even(i):
        even_numbers.append(i)
    
print(even_numbers)

even_numbers_filter = filter(even,numbers)

print(list(even_numbers_filter))

Zip

The zip object yields n-length tuples, where n is the number of iterables passed as positional arguments to zip(). The i-th element in every tuple comes from the i-th iterable argument to zip(). This continues until the shortest argument is exhausted.

If strict is true and one of the arguments is exhausted before the others, raise a ValueError.

squares = [1,4,9,16,25]
cubes = [1,8,37,64,125]

squres_cubes = zip(squares,cubes)

print(list(squres_cubes))

Combined Output

(base) pradeep:~$/usr/local/bin/python3 /Users/pradeep/LearnPython/map_filter_zip_lists.py
[1, 4, 9, 16, 25]
[1, 4, 9, 16, 25]
[2, 4]
[2, 4]
[(1, 1), (4, 8), (9, 37), (16, 64), (25, 125)]
(base) pradeep:~$

As we can see, we get the same output with and without the use of map and filter.