![what is the difference between [[],[]] and [[]] * 2](https://liberty.io/uploads/what-is-the-difference-between-and-2_720.jpg)
t0 = [[]] * 2 t1 = [[], []] t0[0].append('hello') print t0 t1[0].append('hello') print t1 The result is
[['hello'], ['hello']] [['hello'], []] But I can't tell their difference.
2 Answers
When you do [[]] * 2, it gives you a list containing two of the same list, rather than two lists. It is like doing:
a = [] b = [a, a] The usual way to make a list containing several different empty lists (or other mutable objects) is to do this:
t1 = [[] for _ in range(5)] [[]] * 2 makes a shallow copy. Equivalent to:
x = [] t0 = [x, x] However
t1 = [[], []] Uses two separate empty list literals, they are completely different so mutating one obviously doesn't mutate the other
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