1. Function to replace first occurance of 20 with 200¶

In [9]:
def replace_20_with_200(lst, find_num, replace_num):
    for i in range(len(lst)):
        if lst[i] == find_num:
            lst[i] = replace_num
            break
    return lst


lst = [5, 10, 15, 20, 25, 50, 20]

replace_20_with_200(lst, 20, 200)
Out[9]:
[5, 10, 15, 200, 25, 50, 20]

2. Given a Python list, write a program to remove all occurrences of item 20.¶

In [10]:
lst = [5, 20, 15, 20, 25, 50, 20]

def remove_all_20s(lst, element):
    count = lst.count(element)
    for i in range(count):
        lst.remove(element)
    return lst

remove_all_20s(lst, 20)
Out[10]:
[5, 15, 25, 50]

3. Given a two Python list. Write a program to iterate both lists simultaneously and display items from list1 in original order and items from list2 in reverse order.¶

In [11]:
def print_lists(lst1, lst2):
    if len(lst1) != len(lst2):
        print("Both lists should be of same size. Exiting the function.")
    else:
        for i in range(len(lst1)):
            print(lst1[i], lst2[-(i+1)])
            
lst1 = [10, 20, 30, 40]
lst2 = [100, 200, 300, 400]
                
print_lists(lst1, lst2)

10 400
20 300
30 200
40 100
In [ ]: