Answer 1

Extend method takes an iterable and adds each element from that iterable to the end of the list.
a= [1,2,3,4]
b= [5,6,7,8]
a.extend(b) # [1,2,3,4,5,6,7,8]

Append just adds whatever you pass as an argument to the end of the list.

a.append(b) #[1,2,3,4,[5,6,7,8]] note that it's added entire list rather than each of its elements.