Collections¶
Collections are data structures used to store multiple values in a single variable.
Python provides four main built-in collection types:
- List
- Tuple
- Dictionary
- Set
List¶
A list is ordered and changeable (mutable). It allows duplicate values.
fruits = ["apple", "banana", "orange"]
print(fruits)
print(fruits[0])
Modify List¶
fruits = ["apple", "banana", "orange"]
fruits.append("grape")
fruits[1] = "mango"
print(fruits)
Output¶
['apple', 'mango', 'orange', 'grape']
Tuple¶
A tuple is ordered but immutable (cannot be changed after creation).
point = (10, 20)
print(point)
print(point[0])
Output¶
(10, 20)
10
Key Point¶
- Use tuple when data should not be modified
Dictionary¶
A dictionary stores data in key-value pairs.
user = {
"name": "Alice",
"age": 20
}
print(user)
print(user["name"])
Add or Update Value¶
user["age"] = 21
user["city"] = "Singapore"
print(user)
Output¶
{'name': 'Alice', 'age': 21, 'city': 'Singapore'}
Set¶
A set is unordered and does not allow duplicate values.
numbers = {1, 2, 3, 3, 4}
print(numbers)
Output¶
{1, 2, 3, 4}
Common Operations¶
a = {1, 2, 3}
b = {3, 4, 5}
print(a | b) # Union
print(a & b) # Intersection
print(a - b) # Difference
Comparison of Collections¶
| Type | Ordered | Mutable | Duplicates |
|---|---|---|---|
| List | Yes | Yes | Yes |
| Tuple | Yes | No | Yes |
| Dictionary | Yes (Python 3.7+) | Yes | Keys No, Values Yes |
| Set | No | Yes | No |
Null Check¶
items = []
if items is None:
print("no items were provided")
elif not items:
print("items were provided, but the list is empty")
Summary¶
- Use list for ordered, changeable data
- Use tuple for fixed data
- Use dictionary for key-value mapping
- Use set for unique values