In [9]:
#Find the first occurance of 20 in the given list and replace it with 200

list1=[5,10,15,20,25,50,20]
for index in range(0,len(list1)):
    if list1[index]==20:
        i= index
        break
list2=list1[:i]+[200]+list1[i+1:]
print(list2)     

[5, 10, 15, 200, 25, 50, 20]
In [11]:
#Remove all the occurences of item 20 from the given list

list1=[5,20,15,20,25,50,20]
j=[]
for i in list1:
    if i!=20:
        j.append(i)
print(j)

[5, 15, 25, 50]
In [12]:
# iterate 2 lists at the same time and print list 1 in original order and list 2 in reverse order

list1=[10,20,30,40]
list2=[100,200,300,400]
for i in range (0,len(list1)):
    print(list1[i],list2[-(i+1)])

10 400
20 300
30 200
40 100
In [ ]: