How to use for loop repetition control in python with examples

For loop is used to iterate over elements of a sequence such as string,tuple,list and dictionary etc.

For loops are used for sequential traversal. 

For loop has two forms:-

1.)  for var in list:

         statement 1

         statement 2

         statement 3

2.) for var in list:

        statement 1

        statement 2

      else:

          statement 3

          statement 4

Note:-

• During each iteration var is assigned the next value from the list.
• else block is executed when items in the list get exhauted.
• A for loop can be used to generate a list of numbers using the built-in range() functions.
• range(10)--> Generates numbers from 0 to 9.
• range(10,20)--> Generates numbers from 10 to 19.
• range(10,20,2)--> Generates numbers from 10 to 19 in steps of 2.
• range(20,10,-3)--> Generates numbers from 20 to 11 in steps of -3.

Program 1:Write a program to print the 10 numbers in python.

i=0
num=10
for i in range(i,num):
    print(i)

Output:-

Program 2:Write a python program to print the numbers upto which user want to print.

i=1
num=int(input("enter the number:\n"))
for i in range(0,num):
    print(i,end="")

Output:-

Program 3:Write a program to print the even numbers upto 20 numbers in python.

i=2
num=20
for i in range(0,num,2):
    print(i)

Output:-

Nested for loop in python:-

• Python allows us to use nested for loop inside your python program.
• The inner for loop is executed first where for every iteration of the outer for loop.

Syntax:-

for var1 in list1:

     for var2 in list2:

          statement 1

          statement 2

    statement 3

    statement 4

Program 4:Write a program to print the star(*) triangle in python.

i=0
j=0
num=int(input("Enter the number of row which you want to print: \n"))
for i in range(0,num):
    print(" ")
    for j in range(0,i+1):
        print("*", end=" ")

Output:-

How to use else statement in for loop?:-

• Python allows us to use the else statement with the for loop.
• This else statement will be executed only when all the iterations are exhausted.
• If for loop contains break statement then the else statement will not be executed.

Program 5:Write a program to print the natural numbers in decreasing order in python.

i=0
num=int(input("Enter the number:\n"))
for i in range(num,0,-2):
    print(i,end=" ")
else:
    print("else statement is running")

Output:-

Program 6:Write a program to print the natural numbers in increasing order using break statement in python.

i=0
num=int(input("Enter the number:\n"))
for i in range(0,num,2):
    print(i,end=" ")
    if(i==8):
        break
else:
    print("else statement is running")

Output:-

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