If - Statement

if - else statement is a conditional statement in programming. If the statement is proved to be True, then a given set of code block (statement) are executed. If the statement is proved to be False, then another set of code block or none of the statement are executed.

An if statement is written by using the if keyword.

is_up = "up"
if is_up == "up":
    print("interface is up")

interface is up

The else keyword catches anything which isn’t caught by the preceding conditions.

is_up = "down"
if is_up == "up":
    print("interface is up")
else:
    print("interface is down")

interface is down

Elif Statements

The elif keyword, if the previous conditions were not true, then try this condition. The general expression used to represent the nested if and multi-Way if, elif and else Statements is given below:

is_up = "shut"
if is_up == "up":
    print("interface is up")
elif is_up == "shut":
    print("interface is shut by admin")
else:
    print("interface is down")

interface is shut down by admin

In the code below we can mixed the if condition with input() function:

user = input("Enter your username: ")

if user == "ali":
    print("You are authorized to proceed...")
elif user == "bob":
    print("You are authorized to proceed...")
else:
    print("You are not authorized to proceed...")

Enter your username: bob
You are authorized to proceed...

If- else and Logical Operators

In case of AND, if both the operands are True then condition becomes True. If any of the operators is False then the condition evaluations to False.

num = 0
if num > 0 and num < 10:
    print(num)
else:
    print("Number is out of range")    

Number is out of range

For the OR operator, if any of the two operands are True then condition becomes True. If both operators are False then the condition becomes False.

a = 200
b = 33
c = 500

if a > b or a > c:
  print("At least one of the conditions is True")

At least one of the conditions is True

For the NOT operator, on the other hand, if a condition evaluates to True then it becomes False and vice versa.

Ternary Operator

Pyton ternary operator is commonly known as conditional expressions. These operators evaluate expressions based on a condition being true or false.

Here is an example of using these conditional expressions.

num = True
print(Numbers is true) if num else print(Number is false)

num is True

Note

code above is same as below

num = True
if num:
    print(Number is true)
else:
    print(Numbers is false)

Ternary Operator allows to quickly test a condition instead of a multiline if statement.