Need explain for py code

Question

Hello, I need some explain for this code
a=[1,[2,3]]
b=a[:]
a[0]=3
a[1][1]=5
print(b)
The answer was [1,[2,5]]
I got this wrong cause I expected that b will be linked to a and get same list value.
So what exactly mean when b=a[:] and what it different than b=a
Thanx in advance ^^

Answer 1

a[0] is an integer.
integers are copied by value
-> no impact on b

a[1] is a list.
lists are copied by reference
a[1] and b[1] are identical
-> impact on b

Answer 2

b=a means:
b is a further name for a

b=[:] means b is a copy of a but a different object.

copy is tricky :
copying a number makes a new number
but copying a list means copying reference to list.

So the list [2,5] in a and b is the same object.

Answer 3

Oki got it now ^^ thank you so much