7 Lesser-Known Python Techniques about Lists

 

1. Flatten a Nested List

Flatten a deeply nested list into a single list of elements.

from collections.abc import Iterable

def flatten(lst):

    for item in lst:

        if isinstance(item, Iterable) and not isinstance(item, str):

            yield from flatten(item)

        else:

            yield item

nested_list = [1, [2, 3, [4, 5]], 6]

flat_list = list(flatten(nested_list))

print(flat_list)  

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

2. List of Indices for Specific Value

Get all indices of a specific value in a list.

lst = [10, 20, 10, 30, 10, 40]

indices = [i for i, x in enumerate(lst) if x == 10]

print(indices) 

[0, 2, 4]

3. Transpose a List of Lists (Matrix)

Transpose a matrix-like list (switch rows and columns).

matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

transposed = list(map(list, zip(*matrix)))

print(transposed)  

[[1, 4, 7], [2, 5, 8], [3, 6, 9]]

4. Rotate a List

Rotate the elements of a list by n positions.

def rotate(lst, n):

    return lst[-n:] + lst[:-n]

lst = [1, 2, 3, 4, 5]

rotated_lst = rotate(lst, 2)

print(rotated_lst) 

[4, 5, 1, 2, 3]

5. Find Duplicates in a List

Identify duplicate elements in a list.

from collections import Counter

lst = [1, 2, 2, 3, 4, 4, 4, 5]

duplicates = [item for item, count in Counter(lst).items() if count > 1]

print(duplicates)  

[2, 4]

6. Chunk a List

Split a list into evenly sized chunks.

def chunk(lst, n):

    for i in range(0, len(lst), n):

        yield lst[i:i + n]

lst = [1, 2, 3, 4, 5, 6, 7, 8]

chunks = list(chunk(lst, 3))

print(chunks)  

[[1, 2, 3], [4, 5, 6], [7, 8]]

7. Remove Consecutive Duplicates

Remove consecutive duplicates from a list, preserving order.

from itertools import groupby

lst = [1, 2, 2, 3, 3, 3, 4, 4, 5]

result = [key for key, _ in groupby(lst)]

print(result)  

[1, 2, 3, 4, 5]