python - 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 number into two parts and then compare two numbers. I will choose the smaller number from two of them. I can not use ready functions or different approaches.

Basically, this is my code. But it does not run correctly

#!/usr/local/bin/python2.7

alist=[-45,0,3,10,90,5,-2,4,18,45,100,1,-266,706]
largest=alist[0]
h=len(alist)/2 
m=len(alist)-h

print(alist)

for i in alist:
    if alist[h]>largest:
      largest=alist[h]
      i=i+1
print(largest)

Answer 1

O(n^2) algorithm:

In [79]: alist=[-45,0,3,10,90,5,-2,4,18,45,100,1,-266,706]

In [80]: max(n for n in alist if n!=max(alist))
Out[80]: 100

O(n) algorithm:

In [81]: alist=[-45,0,3,10,90,5,-2,4,18,45,100,1,-266,706]

In [82]: M = max(alist)

In [83]: max(n for n in alist if n!=M)
Out[83]: 100