Append 2d empty lists - Printable Version +- Python Forum (https://python-forum.io) +-- Forum: Python Coding (https://python-forum.io/forum-7.html) +--- Forum: General Coding Help (https://python-forum.io/forum-8.html) +--- Thread: Append 2d empty lists (/thread-30401.html) Append 2d empty lists - NMMST - Oct-19-2020 Hi there! I wanted to store my functions result in a 2d list. The function returns 5 values and has to run 100 times in a for loop. I tried to initiate a storage list by ding this: `list1 = [[]]*5`which returns list1 = [[], [], [], [], []] However, when I want to append to one of those lists inside, all of them get the value appended `list1[0].append(3)`Would return: [[3], [3], [3], [3], [3]] The strange thing is that I am able to add an object to a list and after that, the list becomes appendable ```list1[0] = [1] list1[0].append(3)```returns [[1, 3], [], [], [], []] I solved the problem in a far less elegant way, by initiating a list like this `list1 = [[0],[1],[2],[3],[4]] `and after appending, removing the first values. However, this is not flexible and is time consuming to adjust if the problem changes. Is there a more elegant/simple/flexible way to solve this problem? RE: Append 2d empty lists - bowlofred - Oct-19-2020 Your first line has not made a list of 5 different lists inside, it's made a list with 5 copies of the same list inside. ```>>> l = [[]] * 5 >>> l [[], [], [], [], []] >>> [id(x) for x in l] [4464943816, 4464943816, 4464943816, 4464943816, 4464943816]```Instead you want to create a new list 5 different times. Perhaps: ```>>> l = [[] for i in range(5)] >>> l [[], [], [], [], []] >>> [id(x) for x in l] [4464944008, 4464944648, 4464944456, 4464944328, 4464944200] >>> l[2].append(3) >>> l [[], [], [3], [], []]``` RE: Append 2d empty lists - NMMST - Oct-19-2020 (Oct-19-2020, 09:18 PM)bowlofred Wrote: Your first line has not made a list of 5 different lists inside, it's made a list with 5 copies of the same list inside. ```>>> l = [[]] * 5 >>> l [[], [], [], [], []] >>> [id(x) for x in l] [4464943816, 4464943816, 4464943816, 4464943816, 4464943816]```Instead you want to create a new list 5 different times. Perhaps: ```>>> l = [[] for i in range(5)] >>> l [[], [], [], [], []] >>> [id(x) for x in l] [4464944008, 4464944648, 4464944456, 4464944328, 4464944200] >>> l[2].append(3) >>> l [[], [], [3], [], []]``` Thank you very much! This helps out a lot!