Python Program to Flatten a Nested List – 2024

Hey guys, in this blog we will see a Python Program to Flatten a Nested List.

Example 1: Using List Comprehension

# Python Program to Flatten a Nested List Using List Comprehension

my_list = [[2,1], [1,2, 3], [1, 2, 3, 4, 5, 6, 7]]

flat_list = [num for sublist in my_list for num in sublist]
print(flat_list)

Output

[2, 1, 1, 2, 3, 1, 2, 3, 4, 5, 6, 7]

Example 2: Using Nested for Loops (non pythonic way)

# Python Program to Flatten a Nested List Using Nested for Loops (non pythonic way)

my_list = [[2,1], [1,2, 3], [1, 2, 3, 4, 5, 6, 7]]

flat_list = []
for sublist in my_list:
    for num in sublist:
        flat_list.append(num)

print(flat_list)

Output

[2, 1, 1, 2, 3, 1, 2, 3, 4, 5, 6, 7]

Example 3: Using itertools package

# Python Program to Flatten a Nested List Using itertools package

import itertools

my_list = [[2,1], [1,2, 3], [1, 2, 3, 4, 5, 6, 7]]

flat_list = list(itertools.chain(*my_list))
print(flat_list)

Output

[2, 1, 1, 2, 3, 1, 2, 3, 4, 5, 6, 7]

Example 4: Using sum()

# Python Program to Flatten a Nested List Using sum()

my_list = [[2,1], [1,2, 3], [1, 2, 3, 4, 5, 6, 7]]

flat_list = sum(my_list, [])
print(flat_list)

Output

[2, 1, 1, 2, 3, 1, 2, 3, 4, 5, 6, 7]

Example 5: Using lambda and reduce()

# Python Program to Flatten a Nested List Using lambda and reduce()

from functools import reduce

my_list = [[2,1], [1,2, 3], [1, 2, 3, 4, 5, 6, 7]]
print(reduce(lambda x, y: x+y, my_list))

Output

[2, 1, 1, 2, 3, 1, 2, 3, 4, 5, 6, 7]

Check out our other python programming examples

Abhishek Sharma
Abhishek Sharma

Started my Data Science journey in my 2nd year of college and since then continuously into it because of the magical powers of ML and continuously doing projects in almost every domain of AI like ML, DL, CV, NLP.

Articles: 520

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