Why Do Modifications to One Nested List Affect Others in Python?

Nested List Indices Trouble Solved

In Python, when dealing with nested lists, it's crucial to understand the way lists are passed around, known as "reference passing." Typically, variables hold values independently ("pass by value"), but lists are passed by their memory address ("pass by reference") for efficiency reasons.

For instance, if you have 4 * [0], you create four pointers to the same 0 value in memory. However, if you modify one of these lists, the change propagates to all the other lists. This is because they all point to the same underlying memory location.

In your example, you have 4 [(4 [0])], which means you create four copies of an inner list that contains four zeroes. When you modify some_listi 1 in your loop, you actually modify the underlying list at that memory location, resulting in all four lists being affected.

To resolve this, avoid the second multiplication and use a loop to create a new list of lists:

<code class="python">some_list = [(4 * [0]) for _ in range(4)]</code>

By doing so, you create four distinct lists, each containing four zeroes, preventing unexpected modifications to multiple lists.

The above is the detailed content of Why Do Modifications to One Nested List Affect Others in Python?. For more information, please follow other related articles on the PHP Chinese website!