List Fundamentals

A list stores multiple items in an ordered sequence.

When to use a list

Use a list when:

• you care about order (first, second, third)
• you need duplicates
• you add/remove items often

Creating lists

numbers = [10, 20, 30]
names = ["Tom", "Sarah", "Mike"]
mixed = ["Tom", 25, True]

Indexing (most important)

Index starts from 0.

names = ["Tom", "Sarah", "Mike"]
print(names[0])  # Tom
print(names[1])  # Sarah

Negative indexing

print(names[-1])  # Mike (last item)

Slicing (get a part)

nums = [1, 2, 3, 4, 5]
print(nums[1:4])  # [2, 3, 4]

Add and remove

fruits = ["apple", "banana"]
fruits.append("orange")     # add at end
fruits.insert(1, "grape")   # add at position
print(fruits)

fruits.remove("banana")     # remove by value
last = fruits.pop()         # remove last and return it
print(last)

Beginner mistakes

1. IndexError: accessing out of range

# names[10]  # error

2. Confusing copy with reference

a = [1, 2]
b = a
b.append(3)
print(a)  # [1,2,3] because both point to same list

Fix:

a = [1, 2]
b = a.copy()
b.append(3)
print(a)  # [1,2]

Graph: list mental model

flowchart LR
  A[List] --> B[Index 0]
  A --> C[Index 1]
  A --> D[Index 2]

Remember

• List is ordered and mutable
• Index starts at 0
• Use copy() when you want a real copy