I wonder why append add a number to every list that I have in my list. Not only to that one ([0]) that I have choosen. What's the difference between writing [0] or any other number next to append?
j = [[]] * 5
j[0].append(5) # add 5 to every list on list
j[1].append(4) # what's the diffrence? [1] or [0]; it adds number to every element anyway
print (j)
j.append(0) # add 0 to the main list
print (j)
There is no difference.
j = [[]] * 5
Repeats the same empty list instance five times, once at each index.
IOW, the initial empty list is referenced 5 times.
You could verify this:
id(j[0]) == id(j[1])
To instantiate a different empty list at each index requires a comprehension:
[[] for _ in range(5)]
This happens because your initial list j contains 5 references to the same object (so 5 copies to the same list). That's why everything you append goes to every list.
Instead, if you actually create 5 different sublists:
j = [[] for _ in range(5)]
Then it will work as you expect:
[[5], [4], [], [], [], 0]
