Python Why? Plz help to Explain line 2 & 3

Question

a=[1,[2,3]]
b=a[:]
a[0]=6
a[1][1]=5
print(b)

Answer 1

You need to understand this behavior of reference type objects. (List is a reference type object.)

When you use a reference type in your program, the program does not strictly handle the list self.
The program handles just a reference, a link to the actual list value, the actual list value is stored somewhere else, not in the program.

I don't really know how the program gets and modifies the list values when it's supposed to, but it simply does it somehow.

a[:] makes copy of a, but does not use the same reference, a[:] and a are 2 different objects like you might already know.

Even though b is just a copy of a, its items are original, a's changes does not affect b, but a's items' changes affect b's items.

Answer 2

Thank you Seb, make sense!