For most of the programming languages like C/C++, Java…, else-statement is coupled with if-statement. The else-statement can be used only with the if-statement.
This is not the case with Python. As usual, you are free to use else-statement with if-statement. You can also use else-statement after for or while loop.
But, how does it work?
In Python, if you are using else statement after the loop…
The else-block will not be executed if the break statement is executed inside the loop.
This is really a tricky and exceptional concept. There are many questions asked in job interviews based on this concept.
As a part of this tutorial, you will learn using else-statement after for and while loop in Python.
Let’s take some examples.
The syntax is simple. Write else-block just after for loop.
[python]
for i in range(0,5):
print(i)
else:
print("inside else")
[/python]
What is the output of this program?
Output:
0 1 2 3 4 inside else
Here else-statement is getting executed as there is no break statement inside the for-loop.
We are using range() method to iterate over for-loop.
Now, let’s add break statement inside for loop.
[python]
for i in range(0,5):
if i==3:
break;
print(i)
else:
print("inside else")
[/python]
Execute the program and print the output.
Output:
0
1
2
When i==3 inside for loop, the break statement will be executed. Control will come out of the for-loop and will not execute the else-block.
Now consider while loop.
You can also use else statement with while loop.
[python]
i=0
while i<5:
print(i)
i=i+1
else:
print("inside else")
[/python]
What is the output of this program?
Output:
0 1 2 3 4 inside else
The else-block is executed as there is no break statement inside the while loop.
Now we are adding break statement inside the while loop.
[python]i=0
while i<5:
if i==3:
break
print(i)
i=i+1
else:
print("inside else")
[/python]
Run this program again and see the output.
Output:
0 1 2
As break statement has occurred inside the while-loop, else-block is not executed.
This is a little confusing for many of us. Just to remember- when there is a break, there is no else. When there is no break, there is else.
Note: Python for else and Python while else statements work same in Python 2 and Python 3. You can try running this program in different Python versions.
Related tutorials:
Any doubt? Write in the comment.
I am a Python enthusiast who loves Linux and Vim. I hold a Master of Computer Science degree from NIT Trichy and have 10 years of experience in the IT industry, focusing on the Software Development Lifecycle from Requirements Gathering, Design, Development to Deployment. I have worked at IBM, Ericsson, and NetApp, and I share my knowledge on CSEstack.org.
