Collections in Python
Lists (list)
Lists in Python are ordered, mutable collections. They can hold items of different types and support operations such as adding, removing, and modifying elements.
Characteristics:
- Ordered: Elements have a defined order.
- Mutable: You can change the list after creation.
- Allows duplicates: Lists can contain repeated elements.
Syntax:
my_list = [1, 2, 3, "hello", [4, 5]]
Operations Examples:
# Creating a list
fruits = ["apple", "banana", "cherry"]
# Adding an element
fruits.append("orange")
# Inserting an element at a specific position
fruits.insert(1, "blueberry")
# Removing an element
fruits.remove("banana")
# Accessing an element
print(fruits[0]) # Outputs: 'apple'
# Getting the length of the list
print(len(fruits)) # Outputs: 4
Tuples (tuple)
Tuples are ordered, immutable collections. Once created, tuples cannot be changed.
Characteristics:
- Ordered: Elements have a defined order.
- Immutable: You cannot modify elements after creation.
- Allows duplicates: Tuples can contain repeated elements.
Syntax:
my_tuple = (1, 2, 3, "hello", (4, 5))
Operations Examples:
# Creating a tuple point = (10, 20) # Accessing an element print(point[1]) # Outputs: 20 # Unpacking a tuple x, y = point print(x, y) # Outputs: 10 20 # Getting the length of the tuple print(len(point)) # Outputs: 2
Sets (set)
Sets are unordered, mutable collections designed to store unique elements.
Characteristics:
- Unordered: Elements have no specific order.
- Mutable: You can add or remove elements.
- No duplicates: Sets do not allow repeated elements.
Syntax:
my_set = {1, 2, 3, "hello"}
Operations Examples:
# Creating a set
colors = {"red", "green", "blue"}
# Adding an element
colors.add("yellow")
# Removing an element
colors.discard("green")
# Set operations
set1 = {1, 2, 3}
set2 = {3, 4, 5}
# Union
print(set1 | set2) # Outputs: {1, 2, 3, 4, 5}
# Intersection
print(set1 & set2) # Outputs: {3}
# Difference
print(set1 - set2) # Outputs: {1, 2}
Dictionaries (dict)
Dictionaries are ordered collections (from Python 3.7 onwards) that store key-value pairs.
Characteristics:
- Ordered: Elements are stored in the order of insertion (Python 3.7+).
- Mutable: You can add, remove, or modify elements.
- Unique keys: Keys must be unique within a dictionary.
Syntax:
my_dict = {"name": "Alice", "age": 30, "city": "Paris"}
Operations Examples:
# Creating a dictionary
person = {"name": "Alice", "age": 30}
# Adding an element
person["city"] = "Paris"
# Modifying an element
person["age"] = 31
# Removing an element
del person["city"]
# Accessing a value
print(person["name"]) # Outputs: 'Alice'
# Getting keys and values
print(person.keys()) # Outputs: dict_keys(['name', 'age'])
print(person.values()) # Outputs: dict_values(['Alice', 31])
Collections of Collections
Python also allows the creation of collections of collections, such as lists of dictionaries or sets of tuples.
Examples:
# List of dictionaries
employees = [
{"name": "Alice", "position": "Engineer"},
{"name": "Bob", "position": "Manager"}
]
# Set of tuples
coordinates = {(10, 20), (30, 40), (50, 60)}
Summary
- Lists (list): Ordered and mutable collections, allow duplicates.
- Tuples (tuple): Ordered and immutable collections, allow duplicates.
- Sets (set): Unordered and mutable collections, no duplicates.
Dictionaries (dict): Ordered (Python 3.7+), mutable collections of key-value pairs, unique keys.