Python If Statement: Syntax, Usage, and Examples

In Python, conditional statements like the if statement are control flow statements that run (or skip) blocks of code based on specified conditions.

How to Use Python If Statements

Python If Statement

The most basic type of conditional statements are if statements, sometimes also referred to as if conditions in Python. An if statement executes a block of code only if a specified condition evaluates to True. The syntax of an if statement is simple:

if condition:
	# Execute this code if the condition is True

• if: The keyword that initiates an if statement.
• condition: A boolean expression that the if statement evaluates. If the condition evaluates to True, the if statement’s body executes. If the condition evaluates to False, the if statement’s body gets skipped.

Python If-Else Statement

An if statement can have an optional else clause to form an if-else statement in Python. The else clause (also known as else block) of an if-else statement executes the block of code below the else clause only in case the if statement’s condition evaluates to False.

if condition:
	# Execute this code if the condition is True
else:
	# Execute this code if the condition is False

• if: The keyword that initiates an if statement.
• condition: A boolean expression that the if statement evaluates. If the expression evaluates to True, the if statement’s body executes. If the expression evaluates to False, the if statement’s body is skipped.
• else: The keyword that initiates an else clause.

Python If-Elif-Else Statement

An if statement can have optional elif clauses to form an if-elif statement. Elif clauses can check for additional conditions. As soon as a condition evaluates to True, the block of code below that if or elif clause executes.

if condition1:
	# Execute this code if condition1 is True
elif condition2:
	# Execute this code if condition2 is True
else:
	# Execute this code if condition1 and condition2 are False

• if: The keyword that initiates an if statement.
• condition1: A boolean expression that the if statement evaluates. If the condition evaluates to True, the if statement’s body executes. If the condition evaluates to False, the if statement’s body gets skipped.
• elif: The keyword that initiates an elif clause.
• condition2: A boolean expression that the elif clause evaluates if the previous condition evaluated to False. If the expression evaluates to True, the elif clause’s body executes and any following elif and else clauses are skipped. If the expression evaluates to False, the elif clause’s body gets skipped.
• else: The keyword that initiates an else clause.

Case Statements in Python

Although Python does not have a built-in case statement, you can achieve similar functionality using if-elif-else statements or dictionaries. For example:

# Simulating a case statement with if-elif
fruit = "apple"
if fruit == "apple":
    print("You selected an apple.")
elif fruit == "banana":
    print("You selected a banana.")
else:
    print("Unknown fruit.")

In some programming languages like Java, you would use a switch statement instead of multiple if or elif clauses. However, Python handles this using its flexible conditional statements.

When to Use Python If Statements

The primary use of Python if statements is to make decisions within a program. This decision-making capability is fundamental to creating dynamic and interactive programs.

Directing Program Flow

If statements allow your program to execute different blocks of code depending on various conditions. Therefore, conditional statements like an if-else statement can direct the flow of your program.

# Decision based on user input
user_input = input("Enter 'yes' to continue, anything else to quit: ")
if user_input.lower() == 'yes':
    print("Continuing...")
else:
    print("Exiting...")

Iterating with If Statements

If statements often combine with while loops or for loops to handle repetitive tasks conditionally. For example:

# Using a while loop with if
counter = 0
while counter < 5:
    if counter % 2 == 0:
        print(f"{counter} is even.")
    counter += 1

In this example, the loop iterates over numbers from 0 to 4, printing whether each number is even or odd.

Handling Different Scenarios

If statements enable programs to handle different scenarios. For instance, a program can display different messages based on the success or failure of an operation.

# Handling success or failure
operation_successful = False
if operation_successful:
    print("The operation was successful.")
else:
    print("The operation failed.")

Handling User Input

If statements are crucial for interacting with users, such as validating user inputs or choices and providing appropriate feedback.

# Validating user age
age = int(input("Enter your age: "))
if age < 0:
    print("Invalid age. Age cannot be negative.")
elif age < 18:
    print("You are underaged.")
else:
    print("You are an adult.")

Data Processing

In data-driven applications, if statements allow programs to respond to varying data, adjusting their behavior accordingly.

# Adjusting behavior based on data
stock_price = 150
if stock_price > 100:
    print("Stock price is high.")
elif stock_price > 50:
    print("Stock price is moderate.")
else:
    print("Stock price is low.")

Examples of Python If Statements

Conditions and conditional statements are an essential part of almost every Python program. Here are some common use cases for the different kinds of if statements:

E-commerce Checkout Processes

In an e-commerce platform, if-elif-else statements can determine the final price, including promotions, discounts, and shipping options.

# Applying a discount and calculating shipping
total_price = 150.00
is_member = True
if is_member:
    total_price *= 0.9  # Apply 10% member discount

if total_price > 100:
    shipping_cost = 0  # Free shipping for orders over $100
else:
    shipping_cost = 10

total_price += shipping_cost
print(f"Total price with applicable discounts and shipping: ${total_price:.2f}")

Using Pass Statements with If

In some scenarios, the pass statement is useful to define empty blocks in conditional statements while the code structure is being developed.

# Example of a pass statement
if True:
   pass  # Placeholder for future logic

Tuples in Conditional Logic

Tuples can be used with conditional statements to check for multiple values. For instance:

# Checking for values in a tuple
allowed_values = ("yes", "y", "ok")
user_input = input("Type 'yes' or 'no': ").lower()
if user_input in allowed_values:
    print("Input accepted.")
else:
    print("Invalid input.")

In Python, a tuple is a type of immutable sequence. Beginners often find tuples helpful for storing multiple values that don’t need to change.

User Authentication

The conditional operator is handy for concise decision-making assignments.

# Authenticating a user
stored_password = "user123"
input_password = input("Enter your password: ")

if input_password == stored_password:
    print("Access granted.")
else:
    print("Access denied. Incorrect password.")

Environmental Monitoring Systems

Consider environmental monitoring systems as another example. If statements with elif and else clauses might trigger alerts based on sensor readings, such as temperature, air quality, or water levels.

# Triggering an alert based on sensor reading
water_level_sensor = 85  # in percentage

if water_level_sensor > 80:
    print("Warning: High water level detected!")
elif water_level_sensor < 20:
    print("Alert: Low water level detected.")
else:
    print("Water levels are normal.")

Automated Email Responses

Automation scripts, such as those for customer service, can also use if-else statements. For example, they might generate automated email responses based on the subject or content of received emails.

# Automated email response
email_subject = "Refund Request"

if "refund" in email_subject.lower():
    print("Sending automated response for refund requests.")
else:
    print("Sending to the general inquiries queue.")

Learn More About Python Conditional Statements

Nested Conditional Statements

Python allows for conditional statements within conditional statements, enabling complex decision trees. Nesting conditional statements is particularly useful when decisions depend on multiple conditions.

num = 15
if num > 10:
    if num % 2 == 0:
        print("Number is greater than 10 and even")
    else:
        print("Number is greater than 10 and odd")

Using Logical Operators in Python Conditional Statements

Logical operators allow you to construct more complex boolean expressions in Python. The three primary logical operators are and, or, and not.

The and operator allows you to combine multiple conditions. and requires all conditions to be True for the entire expression to evaluate to True. This makes it particularly useful when a decision depends on the fulfillment of several criteria.

# Both conditions need to be True
if is_adult and has_ticket:
    print("You can enter.")

or requires only one of the conditions to be True for the entire expression to evaluate to True. This makes it useful in scenarios with multiple potential paths to achieve a certain outcome.

# Only one condition needs to be True
if is_vip_member or purchase_amount > 100:
    print("You qualify for free shipping.")

The not operator inverts the truth value of its operand. If a condition is True, adding not in front of it makes it False, and vice versa. This can be particularly helpful for readability, making conditions as clear as possible.

# Inverts the truth value
if not is_form_complete:
    print("Please complete all required fields.")

Short-Circuit Evaluation

If statements and logical operators in Python adhere to the concept of short-circuit evaluation. If the first condition of an expression using the and operator is False, the second condition gets skipped. Similarly, for or, if the first condition is True, the entire expression already evaluates to True.

# If 'condition1' is False, Python won't evaluate 'condition2'
if condition1 and condition2:
    # Execute if both are true

Single-Line If Statements in Python

Python allows you to write simple if statements in a single line for cleaner and more concise code. This is especially useful when you have a quick condition and only one line of code to execute.

The basic syntax for a single-line if statement looks like this:

# Single-line if statement
x = 10
if x > 5: print("x is greater than 5")

You can also use a single-line if-else statement with the following format:

# Single-line if-else statement
x = 10
print("x is greater than 5") if x > 5 else print("x is less than or equal to 5")

Single-line if statements keep your code compact and readable, making them perfect for simple conditions where you want to avoid multiple lines. At the same time, they can be harder to read if the conditions become more complex, so limit their use to straightforward scenarios.

If Statements and Loops

If statements often work in tandem with loops to control flow and logic. They are essential in filtering data, executing specific actions for certain items, and more.

numbers = [1, 2, 3, 4, 5]
for num in numbers:
    if num % 2 == 0:
        print(f"{num} is even")
    else:
        print(f"{num} is odd")

If Statements and Functions

In functions, if statements can return different outcomes based on the function's input parameters. Therefore, if statements can make functions more dynamic and versatile.

def check_temperature(temp):
    if temp > 30:
        return "It's a hot day."
    elif temp > 20:
        return "It's a nice day."
    else:
        return "It's cold."
print(check_temperature(25))  # "It's a nice day."

Truthy and Falsy Values

In Python, some non-boolean values evaluate to True or False, too. Such "truthy" or "falsy" values can be useful in a boolean context. For example, empty sequences and collections evaluate to False, while non-empty ones evaluate to True.

my_list = []
if not my_list:  # This evaluates to True because an empty list is considered False
    print("List is empty.")

Python Conditional Operator

Like many other programming languages, Python also supports conditional expressions, also known as ternary operators. Conditional expressions allow for simple conditional assignments in a single line of code.

age = 20
status = "Adult" if age >= 18 else "Minor"
print(status)  # Outputs: "Adult"