search
Search
Join our weekly DS/ML newsletter layers DS/ML Guides
menu
menu search toc more_vert
Robocat
Guest 0reps
Thanks for the thanks!
close
Comments
Log in or sign up
Cancel
Post
account_circle
Profile
exit_to_app
Sign out
help Ask a question
Share on Twitter
search
keyboard_voice
close
Searching Tips
Search for a recipe:
"Creating a table in MySQL"
Search for an API documentation: "@append"
Search for code: "!dataframe"
Apply a tag filter: "#python"
Useful Shortcuts
/ to open search panel
Esc to close search panel
to navigate between search results
d to clear all current filters
Enter to expand content preview
icon_star
Doc Search
icon_star
Code Search Beta
SORRY NOTHING FOUND!
mic
Start speaking...
Voice search is only supported in Safari and Chrome.
Navigate to
A
A
brightness_medium
share
arrow_backShare
Twitter
Facebook
0
thumb_down
0
chat_bubble_outline
0
auto_stories new
settings

Python | if else statement

Control Flow
schedule Jul 1, 2022
Last updated
local_offer Python
Tags
tocTable of Contents
expand_more

Similar to the if statement, the if else statement in Python allows us to perform certain actions if a particular expression evalutes to true. However, unlike the if statement, the if else statement allows us to perform a separate action in the case the test expression evaluates to false.

Syntax

if test expr:
   # code to execute if test expr evaluates to true
else:
   # code to execute if test expr evalutes to false

More concise syntax:

(code to execute if true) if test expr else (code to execute if false)

Example

If-else

To tell a person whether they are old enough or not to buy alcohol:

age = 19
if age >= 20:
   print("Old enough")

else:
   print("Too young")
Too young

The equivalent to above using concise syntax:

age = 19
print("Old enough") if age >=20 else print("Too young")
Too young

If-elif-else

We can also specify multiple scenarios using if-elif-else statements:

age = 9
if age >= 20:
print("We can confirm you are old enough to buy alcohol.")

elif 10 <= age < 20:
print("Sorry you are too young to buy alcohol. Come back when you are 20.")

else:
   print("Where are your parents? You shouldn't be wondering around alone!")
Where are your parents? You shouldn't be wondering around alone!

Running the above code with age=15:

age = 15
if age >= 20:
print("We can confirm you are old enough to buy alcohol.")

elif 10 <= age < 20:
print("Sorry you are too young to buy alcohol. Come back when you are 20.")

else:
   print("Where are your parents? You shouldn't be wondering around alone!")
Sorry you are too young to buy alcohol. Come back when you are 20.

In this way we can specify as many conditions as we want using multiple elif blocks.

NOTE

The else block is a catch all statement. It will execute when none of the conditions above it has been met. This means in some cases, even if the input data is invalid, the else block will execute. Therefore, it is possible to omit the else block and use elif blocks to make sure the input data matches a particular condition before executing.

For example, in our current program a negative age will still result in the else block executing:

age = -15
if age >= 20:
print("We can confirm you are old enough to buy alcohol.")

elif 10 <= age < 20:
print("Sorry you are too young to buy alcohol. Come back when you are 20.")

else:
   print("Where are your parents? You shouldn't be wondering around alone!")
Where are your parents? You shouldn't be wondering around alone!

Obviously a negative age does not make sense so we can remove the else block and replace with elif:

age = -15
if age >= 20:
print("We can confirm you are old enough to buy alcohol.")

elif 10 <= age < 20:
print("Sorry you are too young to buy alcohol. Come back when you are 20.")

elif 0 <= age < 10:
print("Where are your parents? You shouldn't be wondering around alone!")

elif age < 0:
   print("We think you input your age wrong, please try again")
We think you input your age wrong, please try again
mail
Join our newsletter for updates on new DS/ML comprehensive guides (spam-free)
robocat
Published by Arthur Yanagisawa
Edited by 0 others
Did you find this page useful?
Ask a question or leave a feedback...
0
thumb_down
0
chat_bubble_outline
0
settings
Enjoy our search
Hit / to insta-search docs and recipes!