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Using else conditional statement with for loop in python

In most of the programming languages (C/C++, Java, etc), the use of else statement has been restricted with the if conditional statements. But Python also allows us to use the else condition with for loops.

The else block just after for/while is executed only when the loop is NOT terminated by a break statement.

Else block is executed in below Python 3.x program:

for i in range(1, 4):
    print(i)
else# Executed because no break in for
    print("No Break")

Output :

1
2
3
No Break

Else block is NOT executed in below Python 3.x program:



for i in range(1, 4):
    print(i)
    break
else: # Not executed as there is a break
    print("No Break")

Output :

1

Such type of else is useful only if there is an if condition present inside the loop which somehow depends on the loop variable.

In the following example, the else statement will only be executed if no element of the array is even, i.e. if statement has not been executed for any iteration. Therefore for the array [1, 9, 8] the if is executed in third iteration of the loop and hence the else present after the for loop is ignored. In case of array [1, 3, 5] the if is not executed for any iteration and hence the else after the loop is executed.

# Python 3.x program to check if an array consists 
# of even number
def contains_even_number(l):
    for ele in l:
        if ele % 2 == 0:
            print ("list contains an even number")
            break
  
    # This else executes only if break is NEVER
    # reached and loop terminated after all iterations.
    else:     
        print ("list does not contain an even number")
  
# Driver code
print ("For List 1:")
contains_even_number([1, 9, 8])
print (" For List 2:")
contains_even_number([1, 3, 5])

Output:

For List 1:
list contains an even number

For List 2:
list does not contain an even number

As an exercise, predict the output of following program.

count = 0
while (count < 1):    
    count = count+1
    print(count)
    break
else:
    print("No Break")

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.



This article is attributed to GeeksforGeeks.org

tags:

Python

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