05 How to Use List in Python + Tips (Video in Khmer)

Hello friend! 👋 You want keep many value in one variable? Use list!

In this post, I show you how to use list in Python. Easy and short. 🐍

📋 What is List?

List is a group of value in one variable. Use [ ] and put , between value.

fruits = ["apple", "banana", "orange"]

print(fruits)

Output:

['apple', 'banana', 'orange']

List can keep text, number, or mix both.
List keep the order.
List can change (add, remove, edit).

mix = ["Dara", 20, True, 1.75]

🎥 Video: Introduction to List in Python (Khmer)

🔢 Get Item by Index

Index start from 0, not 1.

fruits = ["apple", "banana", "orange"]

print(fruits[0])    # apple   (first)
print(fruits[1])    # banana
print(fruits[-1])   # orange  (last)

✂️ Slice

nums = [10, 20, 30, 40, 50]

print(nums[1:3])    # [20, 30]
print(nums[:2])     # [10, 20]
print(nums[2:])     # [30, 40, 50]

[1:3] mean start at index 1, stop before index 3.

✏️ Change, Add and Remove

fruits = ["apple", "banana"]

fruits[0] = "mango"          # change
fruits.append("orange")      # add at end
fruits.insert(1, "kiwi")     # add at position 1
print(fruits)                # ['mango', 'kiwi', 'banana', 'orange']

fruits.remove("banana")      # remove by value
last = fruits.pop()          # remove last, and give it back
del fruits[0]                # remove by index
print(fruits)                # ['kiwi']

Method	What it do
`append(x)`	Add `x` at end
`insert(i, x)`	Add `x` at index `i`
`remove(x)`	Remove first `x`
`pop()`	Remove last item
`clear()`	Remove all item

🔁 Loop Over List

fruits = ["apple", "banana", "orange"]

for fruit in fruits:
    print(fruit)

Need index too? Use enumerate():

for i, fruit in enumerate(fruits):
    print(i, fruit)

Output:

0 apple
1 banana
2 orange

🎥 Video: Using List in Python Example 2 (Khmer)

🧰 Useful List Function

nums = [5, 2, 8, 1]

print(len(nums))     # 4      how many item
print(max(nums))     # 8
print(min(nums))     # 1
print(sum(nums))     # 16
print(2 in nums)     # True   check item exist

nums.sort()
print(nums)          # [1, 2, 5, 8]

nums.reverse()
print(nums)          # [8, 5, 2, 1]

🧩 Join Two List

a = [1, 2]
b = [3, 4]

print(a + b)         # [1, 2, 3, 4]

❌ Common Error

Index too big:

fruits = ["apple", "banana"]
print(fruits[2])

Error:

IndexError: list index out of range

Fix: list with 2 item only have index 0 and 1. Use len(fruits) to check.

Remove item that not exist:

fruits.remove("mango")

Error: ValueError: list.remove(x): x not in list. Check with in first.

if "mango" in fruits:
    fruits.remove("mango")

Copy list wrong way:

a = [1, 2, 3]
b = a          # not real copy!
b.append(4)
print(a)       # [1, 2, 3, 4]  a change too!

Fix: use b = a.copy().

💡 Tips

Use plural name for list: students, fruits, prices.
Remember: index start from 0.
Use negative index -1 to get last item fast.
Use append() to add item. Use for loop to read all item.
Use len() to count item before use index.
sort() change the original list. Use sorted(nums) if you want keep original.
Use copy() when you want new list, not same list.
Use list comprehension for short code: squares = [n * n for n in range(5)]

❓ Any Question?

Tell us in comment below! 👇

#Python #List #DataTypes #LearnPython #Beginner