Can anyone help me with understanding this please? I’m using a while loop to increment an integer within a list and then i’m trying to add the list to another list to create a list of lists. The list of lists has the expected number of elements but they all show the incremented integer as it would be at the end of the while loop not at each iteration of the while loop.

Here’s what I’ve tried:

my_start_list = [1, 2, 3, 4]
my_end_list = []

while my_start_list[0] != 6:
    my_start_list[0] += 1
    my_end_list.append(my_start_list)

print(my_start_list)
print(my_end_list)

and here’s what i get:

[6, 2, 3, 4]
[[6, 2, 3, 4], [6, 2, 3, 4], [6, 2, 3, 4], [6, 2, 3, 4], [6, 2, 3, 4]]

And I was kind of expecting:

[6, 2, 3, 4]
[[2, 2, 3, 4], [3, 2, 3, 4], [4, 2, 3, 4], [5, 2, 3, 4], [6, 2, 3, 4]]

Can anyone explain what is going on here or point me in a direction that could explain this?

>Solution :

Here the list you are appending is working as a pointer rather than an separate entity. so you need to hard copy the list at each iteration.

my_start_list = [1, 2, 3, 4]
my_end_list = []
c = []

while my_start_list[0] != 6:
    my_start_list[0] = my_start_list[0] + 1
    c = my_start_list.copy()
    my_end_list.append(c)

print(my_start_list)
print(my_end_list)

Output:

[6, 2, 3, 4]
[[2, 2, 3, 4], [3, 2, 3, 4], [4, 2, 3, 4], [5, 2, 3, 4], [6, 2, 3, 4]]
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