Control Flow (If-Else)

Control flow allows your program to branch and take different paths based on specific conditions. In Python, this is handled by if, elif (short for else-if), and else.

1. The Structure

Python relies on indentation to determine which lines of code belong to which branch. A colon : always follows the condition.

2. Comparison Operators

Conditions usually involve comparing values:

• == (Equal), != (Not equal)

• > (Greater than), < (Less than)

• >= (Greater or equal), <= (Less or equal)

3. Logical Operators

You can combine multiple conditions using and, or, and not.

# A simple grading system
score = int(input("Enter your test score (0-100): "))

if score >= 90:
    print("Grade: A")
    print("Excellent work!") # Indented: runs if score >= 90
elif score >= 80:
    print("Grade: B")
    print("Well done.")
elif score >= 70:
    print("Grade: C")
else:
    print("Grade: F")
    print("Keep studying, you can do it!")

# One-liner "Ternary" operator
# Syntax: value_if_true if condition else value_if_false
status = "Pass" if score >= 70 else "Fail"
print(f"Final Status: {status}")

Key Takeaways

• No Parentheses: Unlike C or Java, Python doesn't require () around the condition, though you can use them for clarity in complex expressions.

• Elif: You can have as many elif blocks as you need, but only one if and one else.

• Indentation Matters: If you forget to indent the code inside a branch, Python will throw an IndentationError.