list operations

Question

What is the result of this code?
nums = [10, 9, 8, 7, 6, 5]
nums[0] = nums[1] - 5
if 4 in nums:
print(nums[3])
else:
print(nums[4])

How does this works?

Answer 1

nums = [10, 9, 8, 7, 6, 5]
nums[0] = nums[1] - 5 # change 1st element with 2nd element minus 5 (9 - 5 -> 4)
print(nums) # see how <nums> had changed, 1st element is now 4, not 10 anymore
if 4 in nums: # does <num> contain 4? yes
print(nums[3])
# print the 4th list element -> 7
else:
# if <nums> doesn't contain 4
print(nums[4])
# print the 5th list element -> 6

Answer 2

What don't you understand ? The "in" ?