List of lists weird python issue

Question

list= []

x = ['A', 'B', 'C', 'D', 'E', 'F', 'G']

for i in range(2):

          list.append(x)

list[0][0]="x"

print list

And after printing I get this:

[['x', 'B', 'C', 'D', 'E', 'F', 'G'], ['x', 'B', 'C', 'D', 'E', 'F', 'G']]

The first item in every list was replaced by 'x' whereas I only wanted the first item in the first list to be replaced by 'x'(hence the line list[0][0]="x")

You add the same list twice to another list: `list.append(x)`. You then change that list. There is only one unique list object in your list of lists. — juanpa.arrivillaga, Feb 09 '18 at 06:49

score 1 · Answer 1 · answered Feb 09 '18 at 06:47

The line list.append(x) adds a reference to x into list. Both sublists end up pointing to the same object (as does x). In fact, doing x[0] = 'x' would have the exact same effect as list[0][0] = 'x'. To make the sub-lists independent, make a copy by doing list.append(x.copy()) or list.append(x[:])

List of lists weird python issue

1 Answers1