Formulating a nested list comprising elements in the same position from another nested list

How can I take a nested list and re-formulate it into a new nested list in which:

• the first list of the new nested list, B, comprises the first element of all of the lists within the nested list A.
• the second list of the new nested list, B, comprises the second element of all of the lists within the nested list A.
• the nth list of the new nested list, B, comprises the nth element of all of the lists within the nested list A.

Examples are:

A = [[100,200,300], [400,500,600], [1000,1500,300]]

such that B becomes:

B = [[100,400,1000], [200,500,1500], [300,600,300]]

Of course, in reality A contains hundreds of lists not just three. So i need a method to automate this for large numbers of lists.

>Solution :

If you are sure that all the inner lists have the same length, then

B = [[inner_list[i] for inner_list in A] for i in range(len(A))]

Otherwise you can additionnaly check if index i is not out of bounds for current inner list:

B = [
    [inner_list[i] if i < len(inner_list) else None for inner_list in A]
    for i in range(len(A))
]