Función para encontrar el segundo elemento más grande en python

Programa en Python para encontrar la segunda más grande

# Python program to find second largest
# number in a list
 
# list of numbers - length of
# list should be at least 2
list1 = [10, 20, 4, 45, 99]
 
mx=max(list1[0],list1[1])
secondmax=min(list1[0],list1[1])
n =len(list1)
for i in range(2,n):
    if list1[i]>mx:
        secondmax=mx
        mx=list1[i]
    elif list1[i]>secondmax and \
        mx != list1[i]:
        secondmax=list1[i]
 
print("Second highest number is : ",\
      str(secondmax))