I need some explanation for the following results(in python 2.7)

Question

>>>a=[[0]*2]*2
>>>a[0][0]=5
>>>a
[[5,0],[5,0]]

why does in outer list has repeated elements but not in inner list ?

i expected the result to be
[[5,5],[5,5]] as i used repetition for inner as well as outer loop.

Answer 1

see code : https://code.sololearn.com/cbss5IFkuyAh/?ref=app
Lists are mutable, and elements of the outer list are in fact pointers to the (same) inner list location in memory.

Answer 2

someone correct me if i am rwong but doesn't >>>a=[[0]*2]*2 get executed first then >>>a[0][0]=5,so the list gets created then updated

Answer 3

this is because the repetition operator on a list of one element creates a list of independent items
y=[1]*3
y[0]=5
print(y)
>>>> [5,1,1]

Answer 4

thanks @ifl

Answer 5

@Tejas yes that's correct, the list is created then updated.