Control Flow in Python: Making Decisions with if, elif, else

Control flow is one of the most important aspects of programming. It allows your code to make decisions based on conditions. In Python, this is mainly done using if, elif, and else statements.

These constructs enable your program to execute different blocks of code depending on whether a condition is True or False.

How Control Flow Works in Python

if: Runs a block of code if a condition is true.
elif: Short for "else if", it checks another condition if the previous one was false.
else: Executes a block of code when none of the previous conditions are true.

Example 1: Basic if Statement

age = 20

if age >= 18:
    print("You are an adult")

This prints the message because the condition age >= 18 is True.

Example 2: if-else Statement

temp = 35

if temp > 30:
    print("It's hot outside")
else:
    print("Weather is pleasant")

If the condition is not met, the else block is executed.

Example 3: if-elif-else Chain

score = 75

if score >= 90:
    print("Grade A")
elif score >= 70:
    print("Grade B")
elif score >= 50:
    print("Grade C")
else:
    print("Fail")

Only the first true condition is executed. This is useful for range checks.

Example 4: Nested if Statements

age = 21
has_id = True

if age >= 18:
    if has_id:
        print("Entry allowed")
    else:
        print("ID required")
else:
    print("Not allowed")

Nested conditions help when decisions depend on multiple levels of logic.

Example 5: Using Boolean Variables

is_logged_in = False

if not is_logged_in:
    print("Please log in")

Boolean flags are often used in control flow for user sessions, feature toggles, etc.

Example 6: Multiple Conditions with and/or

age = 22
has_ticket = True

if age >= 18 and has_ticket:
    print("Access granted")

Logical operators like and and or can combine multiple checks.

Example 7: Comparing Strings in Conditions

user_input = "yes"

if user_input == "yes":
    print("You agreed")

String values are commonly used in user inputs and settings checks.

Example 8: Conditional Expressions (Ternary)

marks = 85
result = "Pass" if marks >= 40 else "Fail"
print(result)

Python allows short if-else expressions in a single line.

Best Practices

Use indentation consistently (Python uses indentation instead of curly braces).
Keep conditions readable — use parentheses if needed for clarity.
Use boolean expressions directly without comparing to True or False.

Summary

if: Checks a condition and executes code if it is true.
elif: Checks another condition if previous ones failed.
else: Executes when none of the above conditions are true.
Logical operators like and, or, and not help build complex conditions.

Control flow is what gives your program decision-making ability. Mastering it is essential for building anything from a calculator to a full-fledged web application.

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