E. Loops and Lists

🎯 Learning Goals

By the end of this lesson, you'll be able to:

○ Be able to use a list together with a loop
○ len() function to check the length of a list
○ Be able to process all bullets/enemies in a game

Core Concepts

Iterating over a list

🔄 Analogy: standing in line

Just like People standing in lineLike checking them one person at a time! It processes every item in the list one by one.

fruits = ["Apple", "Banana", "Orange"]

for fruit in fruits:
    print(fruit)

# Output:
# 사과
# 바나나
# 오렌지

The len() function

len() function returns the number of items in a list.

fruits = ["Apple", "Banana", "Orange"]
print(len(fruits))  # 3

Using it in games

# Move all bullets
for bullet in bullets:
    bullet.position += bullet.forward * speed

# Check whether any enemies remain
if len(enemies) == 0:
    print("Victory!")

Example Code

from ursina import *

app = Ursina()

bullets = []
targets = []

# Create targets
for i in range(6):
    target = Entity(
        model='cube',
        color=color.white,
        position=(i*2 - 5, 0, 5)
    )
    targets.append(target)

def update():
    # Move all bullets
    for bullet in bullets:
        bullet.z += 0.5  # Move forward

    # Check for victory
    if len(targets) == 0:
        print("All targets removed!")

EditorCamera()
app.run()

What Happens

All bullets are processed with a loop!

List function summary

Function	Role	Example
`append()`	Add	`my_list.append(item)`
`remove()`	remove	`my_list.remove(item)`
`len()`	Count	`len(my_list)`

Quiz

Quiz: List length

Which function checks the number of items in a list?

Show Answer

Answer: C) len()

len() is short for "length." It returns the number of items in a list, string, and so on!

print(len([1, 2, 3]))  # 3
print(len("hello"))    # 5

Loop and list practice:

fruits = ["사과", "바나나", "오렌지"] Given a list:

To process every item one by one: for fruit fruits:
To check the number of items in the list (3): (fruits) → 3
Check whether the list is empty: if len(fruits) == :

Try Coding It Yourself

Take what you learned with the blocks and write it yourself in Python code!

Iterating over a list

Print every item in the list with a for loop.

Example Answer

fruits = ['Apple', 'Banana', 'Orange']
for fruit in fruits:
    print(fruit)

Result: 사과, 바나나, and 오렌지 are each printed on their own line!

Checking the count with len()

Use the len() function to check the number of items in a list!

Congratulations! 🎉

You've mastered lists!

Things you can do now:

✅ Creating an empty list []
✅ Adding items append()
✅ Removing items remove()
✅ Checking the count len()
✅ Using it together with a loop

Challenge

Challenge 1: ⭐ Easy

for loop to add up all the numbers in the list and print the total.

Hint: total = 0 to start, then add each number.

Challenge 2: ⭐ Easy

Add 5 items to the list and len() to check the count.

Hint: append() 5 times.

Challenge 3: ⭐⭐ Medium

Print each item in the list next to its index number.

Hint: enumerate() function, or range(len(list)) use it.

Challenge 4: ⭐⭐ Medium

Combine two lists into one.

Hint: + operator lets you join lists together.

Challenge 5: ⭐⭐⭐ Hard

Move only the items at or above a certain value into a new list.

Hint: if An if statement and append() use them together.

Challenge 6: ⭐⭐⭐ Hard - Shooting game

On a mouse click, add a bullet bullets to the list
update() move all bullets
When a bullet collides with a target, remove both
Print "Victory!" when all targets are removed

Hint: distance_to() method lets you detect collisions.

🧩 Key Takeaways

What you learned in this lesson:

Concept	Description
for item in list	Iterate over every item in a list
len()	Check the number of items
Usage	Process all bullets/enemies
Victory condition	`len(enemies) == 0`

Review Checklist

[ ] Do you know how to iterate over a list with a loop?
[ ] len() Can you explain the role of the function?
[ ] Do you understand how lists and loops are used in games?

← D. Removing with remove() ⏱️ 7 min