Making Decisions: Booleans & Conditionals

🧠 Mental Model: Programs as Decision Trees

The Fork in the Road

Every conditional statement is like a fork in the road. Your program examines a condition (asks a yes/no question), then chooses which path to take based on the answer.

Condition - The question being asked (True or False?)
If path - What to do when the answer is True
Else path - What to do when the answer is False

Decision Tree Example

Is it raining? 🌧️

True
Take umbrella ☂️

False
Wear sunglasses 🕶️

✅❌ Boolean Logic: The Language of Decisions

Boolean logic is the foundation of all computer decision-making. Every condition ultimately evaluates to either True or False - there's no "maybe" in computer logic!

True

Yes, On, 1

False

No, Off, 0

Interactive Boolean Explorer

Try different comparisons and see their boolean results:

Result:

Enter values and click 'Evaluate'

⚠️ Critical Pitfall: Python's "Truthiness"

Dangerous Assumption: Everything is True or False

Beginner trap: Python considers some non-boolean values as "falsy" and others as "truthy" when used in conditions. This can lead to unexpected behavior!

❌ "Falsy" Values

False - obviously false
0 - zero is false
"" - empty string is false
[] - empty list is false
None - nothing is false

✅ "Truthy" Values

True - obviously true
1, 5, -3 - any non-zero number
"hello" - any non-empty string
[1, 2] - any non-empty list

🧠 Safe Practice

As a beginner, always be explicit! Use comparison operators like == 0 instead of relying on truthiness. It makes your intent crystal clear.

🔀 if-elif-else: The Decision Making Structure

The Complete Decision Framework

if - "If this condition is true, do this"
elif - "Otherwise, if this other condition is true, do this"
else - "If none of the above were true, do this as a fallback"

Interactive Grade Calculator

Let's build a grade calculator that demonstrates if-elif-else chains:

score = 85  # Try changing this!

if score >= 90:
    grade = "A"
    print("Excellent work!")
elif score >= 80:
    grade = "B" 
    print("Good job!")
elif score >= 70:
    grade = "C"
    print("You passed!")
else:
    grade = "F"
    print("Need to study more!")

print(f"Your grade is: {grade}")

Enter a score (0-100):

Enter a score and click 'Calculate Grade'

🔗 Logical Operators: Combining Conditions

Sometimes you need to combine multiple conditions. Python provides three logical operators that work like their English counterparts:

and

Both conditions must be True

age >= 18 and has_license

Can drive only if BOTH are true

or

At least one condition must be True

is_weekend or is_holiday

Don't work on weekends OR holidays

not

Flips True to False, False to True

not is_raining

Go outside if it's NOT raining

Logical Operator Playground

Try different combinations and see how logical operators work:

Condition 1:

Operator:

Condition 2:

Click 'Evaluate Logic' to see the result

🎯 Mastery Check: Boolean Logic & Conditionals

Question 1: Boolean Evaluation

What does this expression evaluate to: 5 > 3 and 2 < 4?

True (both conditions are true)

False

Error

Question 2: Conditional Flow

What gets printed when score = 75?

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

All of them (A, B, C)

🎯 Ready for Repetition!

What You've Mastered

✅ Boolean logic (True/False) as the foundation of decisions
✅ if-elif-else chains for complex decision making
✅ Comparison operators (==, !=, <, >, <=, >=)
✅ Logical operators (and, or, not)
✅ Python's truthiness concept and its pitfalls

Now that your programs can make decisions, let's learn how to make them repeat actions efficiently with loops!

Continue to Repeating Actions →