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]]