How to find second largest number in a list?

Question

So I have to find the second largest number from list. I am doing it through simple loops.

My approach is to divide a list into two parts and then find the largest n

Answer 1

O(n) solution

alist=[-45,0,3,10,90,5,-2,4,18,45,100,1,-266,706]
m = alist[:2] #m will hold 2 values, fill it with the first two values of alist
for num in alist:
    m = sorted(m + [num],reverse=True)[:2] #appends num to m and sorts it, takes only top 2
m[1] #the second highest element.

EDIT: changed to work with negative numbers. Basic description as follows

First I set m to be the first two elements of alist. As I iterate through alist I will be adding one value to the end of m, then sorting the three elements and throwing away the smallest one. This ensures that at the end m will contain the top two largest elements.