3. Python: Conditionals & Loops

🎯 Learning Goals

• Explain the purpose of conditional statements and loops in Python

• Write Python if, elif and else statements

• Use Python for and while loops to repeat tasks

• Apply conditionals and loops to solve problems

📗 Technical Vocabulary

• Conditional statement

• Comparison operators

• Logical operators

• For loop

• While loop

Conditional Statements

age = 17

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

Comparison Operators

x = 5
y = 8

x = 5
y = 8

print(x == y)
print(x != y)
print(x < y)
print(x > y)
print(x <= y)
print(x >= y)

if, elif, and else Statements

Logical Operators

• Returns True only if both conditions are True.

• Returns False, if at least one condition is False.

age = 16
has_permission = True

if age >= 13 and has_permission:
    print("You can create a social media account.")
else:
    print("You cannot create a social media account.")

• Returns True if at least one condition is True.

• Returns False only if both conditions are False.

is_raining = False
will_rain = True

if is_raining or will_rain:
    print("You should bring an umbrella today!")
else:
    print("You do not need an umbrella today.")

• Reverses the boolean value:
• not True → False
• not False → True

is_logged_in = False

if not is_logged_in:
    print("Please log in to continue.")

Loops

1. for Loop (Iterating Over a Sequence)

• Used when you know how many times you need to loop.

• Iterates over a sequence (like a list, tuple, string, or range).

Example: Counting from 1 to 5

for i in range(1, 6):
    print(i)

1
2
3
4
5

Example: Iterating Over a List

fruits = ["apple", "banana", "cherry", "date"]

for fruit in fruits:
    print(fruit)

apple
banana
cherry
date

2. while Loop (Repeating Until a Condition is False)

• Used when you don’t know how many times the loop will run.

• Continues looping as long as the condition is True.

Example: Counting down from 5

count = 5

while count > 0:
    print(count)
    count -= 1  # Decrease count by 1 each time

5
4
3
2
1

Example: User Input with while Loop

correct_password = "python123"
user_input = ""

while user_input != correct_password:
    user_input = input("Enter the password: ")
    
    if user_input == correct_password:
        print("Access granted! ✅")
    else:
        print("Incorrect password. Try again. ❌\n")

Enter the password: abc
Incorrect password. Try again. ❌

Enter the password: hello123
Incorrect password. Try again. ❌

Enter the password: python123
Access granted! ✅

When to Use Each Loop?

gamers = {
	"Nasreen": {
		"favorite_game": "Fortnite",
		"hours_per_week": 10
  },
  "Sophia": {
		"favorite_game": "Minecraft",
		"hours_per_week": 15
  },
  "Kourtney": {
		"favorite_game": "The Sims 4",
		"hours_per_week": 8
  }
}

💼 Takeaways

• Conditional statements allow a program to make decisions based on whether a condition is True or False.
• if → Executes code if a condition is True.
• elif → Adds additional conditions to check if the first condition is False.
• else → Runs if no previous conditions are True.

• Logical operators help combine multiple conditions in conditional statements.
• and → Both conditions must be True
• or → At least one condition must be True
• not → Reverses the boolean value

• Loops allow a program to repeat code without manually writing it multiple times.
• for loop → Used when iterating over a known sequence (lists, ranges, etc.)
• while loop → Used when repeating until a condition is met

For a summary of this lesson, check out the 3. Python: Conditional Statements & Loops One-Pager!