Solution Exercise 53: python algorithm which determines the penultimate index of an element in a list

Exercise 53

Write an algorithm in Python allowing to determine the penultimate index of an element in a list without using any predefined function in Python. Example if L = [2, 7, 11, 7, 21, 39, 7] and a = 7 the algorithm returns 3.

Solution

# function which determines the penultimate index of an element in a list
def penultimate (L, a):
     # initialization of the index list
     lIndex = []
     for i in range (0, len (L)):
          if L [i] == a:
               lIndex.append (i)
     return lIndex [len (lIndex) - 2 ]

# Example
L = [2, 7, 11, 7, 21, 39, 7]
a = 7
print (penultimate (L, a)) # the output:  3