Deleting a desired list in a 2d list

Question

Say I have a 2d list like this:

list = [[1, 2, 3], ["a", 5, 6], [7, 8, 9], [10, 11, 12]]

and I want to delete a list that starts with a. Here is what I tried:

for i in range(0, len(list)):
     if list[i][0] == "a":
          list.pop(i)

Here, I am trying to delete a list that starts with a. However, it gives me an error saying

IndexError: list index out of range

I am not sure what the problem is here. It's weird because when I try print(list[i]), it prints the matching line, which is `["a", 2, 3].

I am expecting list = [[1, 2, 3], [7, 8, 9], [10, 11, 12]] as my final list.

Answer 1

Use a list comprehension:

>>> l = [[1, 2, 3], ["a", 5, 6], [7, 8, 9], [10, 11, 12]]
>>> new_l = [sublist for sublist in l if sublist[0] != 'a']
>>> new_l
[[1, 2, 3], [7, 8, 9], [10, 11, 12]]

通常，在内置变量（list）后面命名变量不是一个好主意，因为您会遮盖这些内置变量。

而且，正如其他人所指出的那样，您最初的问题是list在迭代过程中进行变异。