[[' ']*3]*3 buggy behavior?

[shadowphile]

the inner list [[]*3] produces a list of three lists. But then this list is duplicated three times. However, in python, it's really a list of references that is being multiplied, so the reference is duplicated, but each reference still points to the same underlying list.

solve:

A = [[' ' for _ in range(3)] for _ in range(3)]
B = [[' ',' ',' '],[' ',' ',' '],[' ',' ',' ']]
print(A == B)
A[0][0] = 'X'
B[0][0] = 'X'
print(A)
print(B)

Output:
True
[['X', ' ', ' '], [' ', ' ', ' '], [' ', ' ', ' ']]
[['X', ' ', ' '], [' ', ' ', ' '], [' ', ' ', ' ']]

Thanks for the reply naughtyCat. I'm down to trying to understand when an assignment creates a new object vs references an existing object. Gotta do more reading on this subject. Perhaps immutable objects always get referenced and static things like a string get copied.