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Strange behavior when initializing a list of lists in Python 3


By : Fernanda Morales
Date : September 17 2020, 01:00 AM
I wish did fix the issue. This is built in behavior. When multiplying lists in such fashion, you're not creating new lists, but just copying the references to one initial list, therefore the modification of one of the items leads to others being modified.
See: List of lists changes reflected across sublists unexpectedly
code :


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Strange behavior of lists in python


By : Bejjani Hady
Date : March 29 2020, 07:55 AM
Any of those help When you multiply a list, it copies a reference to the list, it doesn't create a copy of the list. As lists are mutable, when you change it, it is changed for all the references to it.
In ASCII-art terms:
code :
a1 --- [list1, list2] --- list1 = [0, 0]
                      --- list2 = [0, 0]

a2 --- [list3, list3] --- list3 = [0, 0]
>>> a2 = [[0]*2 for _ in range(2)]
>>> a2[0][0] = 1
>>> a2
[[1, 0], [0, 0]]

strange indexing behavior upon initializing a list of dictionaries in python


By : firegarden
Date : March 29 2020, 07:55 AM
Any of those help because you are putting same dict 6 times. [{}]*6 wouldn't copy/deepcopy the original dict but only the reference to it. If you want 6 separate dict use a loop/list comprehension e.g
code :
e = [{} for i in range(6)] 

Strange behavior involving Python nested lists


By : D.Buldakov
Date : March 29 2020, 07:55 AM
I wish this helpful for you I have the following code: , Try this code:
code :
>>> distances[0] is distances[1]
distances = [[100001] * 2] + [[100001] * 2] 
a = [100001, 100001]
b = [100001, 100001]
c = a
distances = a*2 # You will simply get [a, a] 
#so distances[0] cannot be different than distances[1] 
distances = a+b # you will get [a, b]

Python: Initializing and filling a list of lists from another list of lists


By : user3260449
Date : March 29 2020, 07:55 AM
Hope that helps I have a list of lists in Python which contains a tuple For eg. , You can build a_list and b_list using list comprehnsion like this
code :
a_list = [[t[0] for t in row] for row in tuple_list]
b_list = [[t[1] for t in row] for row in tuple_list]

Strange behavior after growing list of lists


By : user3442523
Date : March 29 2020, 07:55 AM
Hope this helps change data = [[]] * len(cols) to data = [[] for i in range(len(cols))] and keep everything same.
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