Python Conditionals 🔀

Making Smart Decisions

Session 2: If, Elif, Else Logic

What Are Conditionals? 🤔

Conditionals are statements that let your program make decisions. "If something is true, do this. Otherwise, do that."

Real-World Examples:

If it's raining, bring an umbrella. Else, don't.
If you're 13 or older, you can watch PG-13 movies. Else, watch G movies.
If your password is correct, log in. Else, show error.

This is the foundation of how apps make decisions!

Comparison Operators 🔍

Before using if statements, you need to compare values. These operators check if something is true or false:

Operators:

== equal to (a == b)
!= not equal to (a != b)
> greater than (a > b)
< less than (a < b)
>= greater than or equal (a >= b)
<= less than or equal (a <= b)

Note: Use == to compare, not = (which assigns values)

The If Statement 🚪

If a condition is true, execute code inside the if block.

Code Example:

age = 15
if age >= 13:
  print("You can watch PG-13 movies!")
                

Notice: Code inside if is indented (pushed right). Indentation matters in Python!

If-Else Statement 🔄

Do one thing if true, something else if false.

Code Example:

password = input("Enter password: ")
if password ==
                    "secret123":
  print("Access granted!")
else:
  print("Access denied!")
                

If password matches, print access granted. Otherwise, print denied.

Elif: Multiple Conditions 🌳

Elif (else if) lets you check multiple conditions. Check the first one, then the next, etc.

Code Example - Grade Calculator:

score = int(input("Your score: "))
if score >= 90:
  print("A -
                    Excellent!")
elif score >= 80:
  print("B - Good job!")
elif score >=
                    70:
  print("C - Okay")
else:
  print("F - Need help")

Logic Operators: AND & OR 🔗

Combine multiple conditions with and and or. Remember logic gates?

AND - Both must be true:

age = 15
if age >= 13 and age < 18:
  print("You are a
                        teenager!")

OR - At least one must be true:

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

Project: Password Checker 🔐

Requirements:

Ask user for password
Check if password is at least 8 characters long
Check if it contains a number
If both true, print "Strong password!"
Otherwise print "Weak password"

Hint: Use len(password) to check length

Project: Grade Calculator 🎓

Code:

score = int(input("Enter score (0-100): "))
if score >=
                    90:
  grade = "A"
elif score >= 80:
  grade = "B"
elif score >=
                    70:
  grade = "C"
elif score >= 60:
  grade =
                    "D"
else:
  grade = "F"
print("Your grade: " + grade)

Common Mistakes to Avoid ❌

Watch Out For:

Using = instead of == in comparisons (= assigns, == compares)
Forgetting indentation (Python needs proper spacing!)
Confusing and/or (and = both true, or = at least one true)
Not converting input to numbers (input() gives text, need int())

What We Learned 🎓

Conditionals make programs make decisions
Comparison operators (==, !=, >, <) check conditions
if/else execute different code based on conditions
elif checks multiple conditions in order
and/or combine multiple conditions (logic gates!)
Indentation matters in Python!
Conditionals are the foundation of smart apps

Smart Programs! 🎉

Your programs can now make decisions

Next Session: Loops - Making Programs Repeat