Intro to if

IF

The if statement allows the execution of code when certain condition is met (True).

General syntax

 `if` condition:
    # body of statement if the condition is True

Caution

Python uses indentation style (i.e., 4 spaces or tabs at the beginning of lines) to define the structure of code statements within loops, functions, and conditional statements

IF/ELSE

Additionally, you can use the else statement to specify an alternative block of code to be executed if the condition is False.

General syntax

if condition:
    # Statement to be executed if the condition is true
else:
    # Statement to be executed if the condition is false

IF/ELSE/ELIF

You can also use multiple elif (i.e., “else if”) statements to specify additional conditions to be checked. The if, else, and elif statements provide a way to control the flow based on specific conditions and executes different blocks, which makes your program more flexible on various situations.

General syntax

if condition1:
    # Statement to be executed if the condition1 is true
elif condition2:
    # Statement to be executed if the condition1 is False and condition2 is True
else:
    # Statement to be executed if all conditions are false

Examples

# Example 1
x = 10

if x > 0:
    print("x is positive")
else:
    print("x is non-positive")

x is positive

# Example 2
x = 10

if x > 0:
    print("x is positive")
elif x < 0:
    print("x is negative")
else:
    print("x is zero")

x is positive

Nested

if statements are placed within the code block of another if statement, and builds additional decision conditions within the block of code executed when the outer if statement’s condition is true.

General syntax

if condition1:
    # Code to be executed if condition1 is true
    if condition2:
        # Code to be executed if both condition1 and condition2 are true
    else:
        # Code to be executed if condition1 is true but condition2 is false
else:
    # Code to be executed if condition1 is false

# Example 3
number = 5

# outer if statement
if (number >= 0):
    # inner if statement
    if number == 0:
        print('Number is 0')

    # inner else statement
    else:
        print('Number is positive')

# outer else statement
else:
    print('Number is negative')

Number is positive