Python: if condition

“if” statement

"if" tell the program execute the section of code when the condition evaluates to true.

Syntax

if_stmt ::=  "if" expression ":" suite

test.py

a=10

if (a < 10) :
 print("a is less than 10")
 
if (a == 10) :
 print("a is equal to 10")
 
if( a > 10) :
 print("a is greater than 10")

$ python3 test.py

a is equal to 10

if-else statement

If the condition true, then if block code executed. other wise else block code executed.

Syntax

if_stmt ::=  "if" expression ":" suite

                   ["else" ":" suite]

test.py

a=10

if (a != 10) :
 print("a is not equal to 10")
else :
 print("a is equal to 10")

if-elif-else statement

By using if-elif-else construct, you can choose number of alternatives. An if statement can be followed by an optional elif...else statement.

Syntax

if_stmt ::=  "if" expression ":" suite

             ( "elif" expression ":" suite )*

             ["else" ":" suite]

test.py

a=10

if (a > 10) :
 print("a is greater than 10")
elif (a < 10) :
 print("a is less than 10")
else :
 print("a is equal to 10")

$ python3 test.py

a is equal to 10

Note:

a. In python, any non-zero integer value is treated as true; zero is false.

test.py

if (100) :
 print("Hello")
else :
 print("Bye")

$ python3 test.py

Hello

b. Any sequence (string, list etc.,) with a non-zero length is true, empty sequences are false.

test.py

list=[]
data="abc"

if (list) :
 print("list is not empty")
else :
 print("list is empty")
 
if (data) :
 print("data is not empty")
else :
 print("data is empty")

$ python3 test.py

list is empty

data is not empty

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