Python for-else Loops

Python supports an optional else block to be associated with a for loop. If a else block is used with a for loop, it is executed only when the for loop terminates normally.

The for loop terminates normally when it completes all its iterations without encountering a break statement, which allows us to exit the loop when a certain condition is met.

Flowchart of For Else Loop

The following flowchart illustrates use of for-else loop −

Syntax of For Else Loop

Following is the syntax of for loop with optional else block −

for variable_name in iterable:
 #stmts in the loop
 .
 .
 .
else:
 #stmts in else clause
 .
 .

Example of For Else Loop

The following example illustrates the combination of an else statement with a for statement in Python. Till the count is less than 5, the iteration count is printed. As it becomes 5, the print statement in else block is executed, before the control is passed to the next statement in the main program.

for count in range(6):
   print ("Iteration no. {}".format(count))
else:
   print ("for loop over. Now in else block")
print ("End of for loop")

On executing, this code will produce the following output −

Iteration no. 1
Iteration no. 2
Iteration no. 3
Iteration no. 4
Iteration no. 5
for loop over. Now in else block
End of for loop

For-Else Construct without break statement

As mentioned earlier in this tutorial, the else block executes only when the loop terminates normally i.e. without using break statement.

Example

In the following program, we use the for-else loop without break statement.

for i in ['T','P']:
   print(i)
else:
   # Loop else statement
   # there is no break statement in for loop, hence else part gets executed directly
   print("ForLoop-else statement successfully executed")

On executing, the above program will generate the following output −

T
P
ForLoop-else statement successfully executed

For-Else Construct with break statement

In case of forceful termination (by using break statement) of the loop, else statement is overlooked by the interpreter and hence its execution is skipped.

Example

The following program shows how else conditions work in case of a break statement.

for i in ['T','P']:
   print(i)
   break
else:
   # Loop else statement
   # terminated after 1st iteration due to break statement in for loop
   print("Loop-else statement successfully executed")

On executing, the above program will generate the following output −

T

For-Else with break statement and if conditions

If we use for-else construct with break statement and if condition, the for loop will iterate over the iterators and within this loop, you can use an if block to check for a specific condition. If the loop completes without encountering a break statement, the code in the else block is executed.

Example

The following program shows how else conditions works in case of break statement and conditional statements.

# creating a function to check whether the list item is a positive
# or a negative number
def positive_or_negative():
   # traversing in a list
   for i in [5,6,7]:
   # checking whether the list element is greater than 0
      if i>=0:
         # printing positive number if it is greater than or equal to 0
         print ("Positive number")
      else:
         # Else printing Negative number and breaking the loop
         print ("Negative number")
         break
   # Else statement of the for loop
   else:
      # Statement inside the else block
      print ("Loop-else Executed")
# Calling the above-created function
positive_or_negative()

On executing, the above program will generate the following output −

Positive number
Positive number
Positive number
Loop-else Executed