Lessons

Python Basics

Python Variables

Operators in Python

Conditional Statements in Python

Python Lists

Python Tuples

Python Sets

Python Dictionaries

Loops in Python

Python Arrays and Functions

Conclusion

Python Dictionaries

Dictionaries in Python

Python dictionaries are powerful data structures used to store data values in key-value pairs. This lesson will explore the characteristics of dictionaries, how to create and manipulate them, and various examples demonstrating their functionality.

1. What is a Dictionary?

A dictionary is a collection that is ordered*, changeable, and does not allow duplicates. As of Python version 3.7, dictionaries maintain the order of items. In earlier versions, dictionaries were unordered.

Dictionaries are defined using curly brackets {} and consist of key-value pairs.

Example: Create and Print a Dictionary

python
1# Creating a dictionary
2car_dict = {
3  "brand": "Tesla",
4  "model": "Model S",
5  "year": 2020
6}
7
8print(car_dict)  # Output: {'brand': 'Tesla', 'model': 'Model S', 'year': 2020}

2. Dictionary Items

Dictionary items are presented in key-value pairs, and you can access them using the key names.

Example: Accessing a Dictionary Value

python
1# Creating a dictionary
2car_dict = {
3  "brand": "Tesla",
4  "model": "Model S",
5  "year": 2020
6}
7
8# Accessing the "model" value
9print(car_dict["model"])  # Output: Model S

3. Ordered or Unordered?

As of Python 3.7, dictionaries are ordered collections. This means that items have a defined order, which will not change. In versions prior to 3.7, dictionaries were unordered.

Example: Checking Order

python
1# Creating a dictionary
2color_dict = {
3  "first": "red",
4  "second": "green",
5  "third": "blue"
6}
7
8print(color_dict)  # Output will show the order of items as defined

4. Changeable

Dictionaries are mutable, meaning you can change, add, or remove items after they have been created.

Example: Modifying a Dictionary

python
1# Creating a dictionary
2person_dict = {
3  "name": "Alice",
4  "age": 30
5}
6
7# Changing the age
8person_dict["age"] = 31
9print(person_dict)  # Output: {'name': 'Alice', 'age': 31}

5. Duplicates Not Allowed

Dictionaries cannot have two items with the same key. If you use the same key again, the value will be overwritten.

Example: Duplicate Key Handling

python
1# Creating a dictionary with a duplicate key
2product_dict = {
3  "name": "Laptop",
4  "price": 1000,
5  "price": 1200  # This will overwrite the previous price
6}
7
8print(product_dict)  # Output: {'name': 'Laptop', 'price': 1200}

6. Dictionary Length

To determine how many items a dictionary contains, use the len() function.

Example: Get the Number of Items in a Dictionary

python
1# Creating a dictionary
2item_dict = {
3  "item1": "Book",
4  "item2": "Pen",
5  "item3": "Notebook"
6}
7
8print(len(item_dict))  # Output: 3

7. Dictionary Items - Data Types

The values in a dictionary can be of any data type, including strings, integers, booleans, and lists.

Example: Dictionary with Various Data Types

python
1# Creating a dictionary with mixed data types
2mixed_dict = {
3  "name": "Bob",
4  "is_student": True,
5  "age": 25,
6  "courses": ["Math", "Science"]
7}
8
9print(mixed_dict)  # Output: {'name': 'Bob', 'is_student': True, 'age': 25, 'courses': ['Math', 'Science']}

8. What is the Data Type of a Dictionary?

From Python's perspective, dictionaries are defined as objects of the data type 'dict'.

Example: Print the Data Type of a Dictionary

python
1# Creating a dictionary
2my_dict = {
3  "brand": "Toyota",
4  "model": "Camry",
5  "year": 2022
6}
7
8print(type(my_dict))  # Output: <class 'dict'>

Frequently Asked Questions