Control Flow - Conditional Statements | Learn Python Free - SkillsetMaster | Learn Data Analytics Free

What You'll Learn

Making decisions with if
Multiple choices with elif
Default option with else
Nested conditions

What are Conditional Statements?

They let your code make choices, like:

"If it's raining, take an umbrella"
"If age is over 18, allow entry"
"If password is correct, log in"

The if Statement

Basic format:

code.py

if condition:
    # do this

Example:

code.py

age = 20

if age >= 18:
    print("You can vote!")

Important: Notice the indentation (spaces)! Python needs it.

if-else Statement

Do one thing or another:

code.py

age = 16

if age >= 18:
    print("You can vote!")
else:
    print("Too young to vote")

Output: Too young to vote

if-elif-else Statement

Multiple choices:

code.py

score = 85

if score >= 90:
    print("Grade: A")
elif score >= 80:
    print("Grade: B")
elif score >= 70:
    print("Grade: C")
else:
    print("Grade: F")

Output: Grade: B

Practice Examples

Example 1: Age check

code.py

age = 25

if age < 13:
    print("You are a child")
elif age < 18:
    print("You are a teenager")
elif age < 65:
    print("You are an adult")
else:
    print("You are a senior")

Example 2: Password check

code.py

password = "secret123"
user_input = "secret123"

if user_input == password:
    print("Access granted!")
else:
    print("Wrong password!")

Example 3: Temperature

code.py

temp = 75

if temp > 80:
    print("It's hot!")
elif temp > 60:
    print("It's nice!")
else:
    print("It's cold!")

Multiple Conditions

Use and and or:

Example: Club entry

code.py

age = 25
has_id = True

if age >= 21 and has_id:
    print("Welcome to the club!")
else:
    print("Sorry, can't enter")

Example: Weekend check

code.py

day = "Saturday"

if day == "Saturday" or day == "Sunday":
    print("It's the weekend!")
else:
    print("It's a weekday")

Nested if Statements

if inside if:

code.py

age = 25
has_license = True

if age >= 18:
    if has_license:
        print("You can drive!")
    else:
        print("You need a license")
else:
    print("You're too young")

Comparing Numbers

code.py

num1 = 10
num2 = 5

if num1 > num2:
    print("num1 is bigger")
elif num1 < num2:
    print("num2 is bigger")
else:
    print("They are equal")

Checking Text

code.py

name = "John"

if name == "John":
    print("Hello John!")
else:
    print("You are not John")

Case sensitive:

code.py

name = "john"

if name == "John":
    print("Hello!")  # Won't print (lowercase j)

Better way:

code.py

name = "john"

if name.lower() == "john":
    print("Hello!")  # Will print!

Real-World Examples

Example 1: Discount calculator

code.py

price = 100
is_member = True

if is_member:
    discount = price * 0.2  # 20% off
    final_price = price - discount
    print("Member price:", final_price)
else:
    print("Regular price:", price)

Example 2: Login system

code.py

username = "admin"
password = "1234"

if username == "admin" and password == "1234":
    print("Login successful!")
else:
    print("Invalid credentials")

Example 3: Grade calculator

code.py

score = 75

if score >= 90:
    grade = "A"
    message = "Excellent!"
elif score >= 80:
    grade = "B"
    message = "Great job!"
elif score >= 70:
    grade = "C"
    message = "Good!"
elif score >= 60:
    grade = "D"
    message = "Passed"
else:
    grade = "F"
    message = "Failed"

print("Grade:", grade)
print(message)

Common Mistakes

Mistake 1: Forgetting colon (:)

code.py

# Wrong
if age > 18
    print("Adult")

# Correct
if age > 18:
    print("Adult")

Mistake 2: Wrong indentation

code.py

# Wrong (no spaces)
if age > 18:
print("Adult")

# Correct (4 spaces)
if age > 18:
    print("Adult")

Mistake 3: Using = instead of ==

code.py

# Wrong (assigns value)
if age = 18:

# Correct (compares)
if age == 18:

Mistake 4: No else after elif

code.py

# This is OK
if score >= 90:
    print("A")
elif score >= 80:
    print("B")
# else is optional!

Short if Statements

One-line version:

code.py

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

Same as:

code.py

if age >= 18:
    status = "Adult"
else:
    status = "Minor"

Quick Reference

Basic if:

code.py

if condition:
    # do this

if-else:

code.py

if condition:
    # do this
else:
    # do that

if-elif-else:

code.py

if condition1:
    # do this
elif condition2:
    # do that
else:
    # do default

Summary

if makes decisions
elif adds more choices
else is the default option
Always use colon (:)
Always indent (4 spaces)
Use and/or for multiple conditions

What's Next?

Now let's learn how to repeat code with for loops!