Python .reverse() and .extend()

Question

I'm a beginner in Python. I try to create a list from 1~5 then print out the reverse list and combine them like [1,2,3,4,5,5,4,3,2,1] and here is my working.

num1 = list(range(1,6))
num2 = num1.reverse()
print(num1)
print(num2)
print(num1.extend(num2))

Output of num1 is reverse [5,4,3,2,1]. Output of num2 is None and the extend function not working. How .reverse() and .extend() really work?

Answer 1

list.reverse()

does the reversal in-place - so your original list is reversed. And also, the reverse() method returns None

Hence your num1 get reversed & num2 is None.

Similarly, extend also modifies the argument list & returns None

To make this work:

num1 = list(range(1,6))
num2 = num1[::-1]
print(num1)
print(num2)
num1.extend(num2)
print(num1)

Gives:

[1, 2, 3, 4, 5]
[5, 4, 3, 2, 1]
[1, 2, 3, 4, 5, 5, 4, 3, 2, 1]