Python for-else Loops

Python - For Else Loop

Python supports an optionalelse block to be associated with afor loop. If aelse block is used with afor loop, it is executed only when the for loop terminates normally.

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

Flowchart of For Else Loop

The following flowchart illustrates use offor-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 inPython. 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 followingoutput −

Iteration no. 1Iteration no. 2Iteration no. 3Iteration no. 4Iteration no. 5for loop over. Now in else blockEnd 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

TPForLoop-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)   breakelse:   # 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 usefor-else construct withbreak statement andif condition, thefor loop will iterate over the iterators and within this loop, you can use anif block to check for a specific condition. If the loop completes without encountering abreak statement, the code in the else block is executed.

Example

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

# creating a function to check whether the list item is a positive# or a negative numberdef 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 functionpositive_or_negative()

On executing, the above program will generate the following output

Positive numberPositive numberPositive numberLoop-else Executed