Conditionals

Python Control Flow: The Traffic Light of Code 🚦

Imagine you’re at a crossroads. Left leads to the park, right leads to school, straight goes to the bakery. How do you decide which way to go? Conditionals in Python work exactly like this — they help your code make decisions!

The Universal Analogy: The Magic Gatekeeper

Think of conditionals as a magic gatekeeper at a castle. The gatekeeper asks questions:

• “Do you have the password?” → If yes, enter!
• “Are you a friend?” → If yes, come in. If no, go away!

Your Python code has its own gatekeeper. Let’s meet them!

1. If Statements: The Simple Question

The gatekeeper asks one question. If the answer is “yes” (True), you get in.

How It Works

age = 10

if age >= 5:
    print("You can ride!")

What happens:

• The gatekeeper checks: “Is age 5 or more?”
• Age is 10. Yes! That’s 5 or more.
• So it prints: You can ride!

The Pattern

if condition:
    # do this when True

Key rule: The code under if only runs when the condition is True.

2. If-Else: Two Doors

Now the gatekeeper has two doors. One for “yes” and one for “no.”

How It Works

has_ticket = False

if has_ticket:
    print("Welcome to the movie!")
else:
    print("Sorry, buy a ticket first!")

What happens:

• Gatekeeper checks: “Do you have a ticket?”
• has_ticket is False (no ticket!)
• Goes through the else door: Sorry, buy a ticket first!

3. If-Elif-Else: Many Doors

Sometimes there are many choices, not just yes or no. Like a restaurant menu!

How It Works

score = 85

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

What happens:

• Is 85 >= 90? No, skip.
• Is 85 >= 80? Yes! Print Grade: B
• Stop checking. We found our answer!

The Flow

graph TD
    A["Start: score = 85"] --> B{score >= 90?}
    B -->|No| C{score >= 80?}
    B -->|Yes| D["Grade: A"]
    C -->|Yes| E["Grade: B"]
    C -->|No| F{score >= 70?}
    F -->|Yes| G["Grade: C"]
    F -->|No| H["Keep trying!"]

4. Ternary Operator: The One-Liner Magic

Sometimes you want to make a quick decision in one line. Like a shortcut!

The Long Way

age = 15
if age >= 18:
    status = "adult"
else:
    status = "minor"

The Shortcut (Ternary)

age = 15
status = "adult" if age >= 18 else "minor"

Result: status is "minor"

The Pattern

value = this_if_true if condition else this_if_false

Think of it as asking: “Is this true? Pick left. Otherwise, pick right.”

5. Truthy and Falsy Values: The Invisible Truth

Here’s a secret: Python doesn’t just check True or False. It checks if things feel true or false!

Falsy Values (Feel False)

These are empty or nothing:

Truthy Values (Feel True)

Everything else! If it has something, it’s truthy.

Real Example

name = ""

if name:
    print(f"Hello, {name}!")
else:
    print("Hello, stranger!")

What happens:

• name is "" (empty string)
• Empty feels falsy
• Prints: Hello, stranger!

Another Example

friends = ["Alice", "Bob"]

if friends:
    print("You have friends!")
else:
    print("Time to make friends!")

What happens:

• friends has items (not empty)
• That feels truthy
• Prints: You have friends!

6. Short-Circuit Evaluation: The Lazy Gatekeeper

This gatekeeper is lazy (in a smart way). They stop checking as soon as they know the answer!

With and — Both Must Be True

has_key = False
door_open = True

if has_key and door_open:
    print("Enter!")

What happens:

• Checks has_key first → It’s False
• Gatekeeper thinks: “If the first is False, both can’t be True!”
• Stops immediately. Doesn’t even check door_open!

With or — One Must Be True

is_vip = True
has_ticket = False

if is_vip or has_ticket:
    print("Welcome!")

What happens:

• Checks is_vip first → It’s True
• Gatekeeper thinks: “One True is enough!”
• Stops immediately. Doesn’t check has_ticket!

Why This Matters

You can use it for safe checks:

items = []

# Safe! Checks if items exist first
if items and items[0] == "apple":
    print("First item is apple!")

If items is empty, Python never tries items[0] (which would crash!).

7. Chained Comparisons: The Elegant Way

Python lets you chain comparisons like math class!

The Old Way

age = 15

if age >= 13 and age <= 19:
    print("You're a teenager!")

The Python Way

age = 15

if 13 <= age <= 19:
    print("You're a teenager!")

Same result, but cleaner!

More Examples

x = 5

# Check if x is between 1 and 10
if 1 < x < 10:
    print("x is in range!")

# Check if all three are equal
a = b = c = 7
if a == b == c:
    print("All equal!")

The Flow

graph TD
    A["age = 15"] --> B{13 <= 15?}
    B -->|Yes| C{15 <= 19?}
    C -->|Yes| D["Teenager!"]
    B -->|No| E["Not a teen"]
    C -->|No| E

Putting It All Together

Let’s build a game entry checker using everything we learned!

age = 14
has_permission = True
coins = 0

# Chain comparison for age
is_right_age = 10 <= age <= 18

# Short-circuit: check coins only if
# age and permission are okay
if is_right_age and has_permission:
    # Ternary for quick message
    msg = "Play!" if coins else "Need coins!"
    print(msg)
elif is_right_age:
    print("Get parent permission!")
else:
    print("Age not allowed.")

What happens:

1. is_right_age → 10 <= 14 <= 18? True!
2. is_right_age and has_permission → True and True? True!
3. coins is 0 → Falsy!
4. Ternary picks: "Need coins!"
5. Prints: Need coins!

Quick Reference Card

You Did It! 🎉

You just learned how Python makes decisions! Remember:

1. If = One question, one action
2. If-Else = Two paths to choose
3. If-Elif-Else = Many paths to choose
4. Ternary = Quick one-line decision
5. Truthy/Falsy = Empty feels false, stuff feels true
6. Short-circuit = Stop checking when you know the answer
7. Chained = Compare multiple things elegantly

Now go write some code that thinks! 🚀