modified-iterating-list / W4701

Message emitted:

Iterated list '%s' is being modified inside for loop body, consider iterating through a copy of it instead.

Description:

Emitted when items are added or removed to a list being iterated through. Doing so can result in unexpected behaviour, that is why it is preferred to use a copy of the list.

Problematic code:

fruits = ["apple", "orange", "mango"]
for fruit in fruits:
    fruits.append("pineapple")  # [modified-iterating-list]

Correct code:

fruits = ["apple", "orange", "mango"]
for fruit in fruits.copy():
    fruits.append("pineapple")

Created by the modified_iteration checker.