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lists in list - kubine - Aug-16-2018
hi I make a list in list and append in [0] index a value. but it appends in all index. can andybody know why?
code:
matrix=[[1]]*3 print(matrix) matrix[0].append(2) print(matrix)output:
Output:[[1], [1], [1]]
[[1, 2], [1, 2], [1, 2]]code:
matrix=[] for i in range(3): ++++list=[1] ++++matrix.append(list) print(matrix) matrix[0].append(2) print(matrix)output:
Output:[[1], [1], [1]]
[[1, 2], [1], [1]]RE: lists in list - ichabod801 - Aug-16-2018
Lists are mutable. When you copy them with
[[3]] * 3 it copies three references to the same list. Use a list comprehension instead: [[3] for sublist in range(3)]. With a list comprehension, the sub-list is reevaluated each time through the loop, giving you three independent sub-lists.