Fundamentals of Python : 5. Python Dictionaries
Fundamentals of Python
5. Python Dictionaries
Dictionaries are a core data structure in Python that store data in key-value pairs. They are incredibly efficient for data lookup, manipulation, and hierarchical data representation. Dictionaries are defined using curly braces { } and allow for rapid access, insertion, and deletion of values using unique keys.
Key Characteristics:
🧭 Ordered (from Python 3.7 onward): Maintains the order in which items are inserted.
🛠️ Mutable: Dictionary contents can be changed (add, update, or delete key-value pairs).
🔑 Unique Keys: Duplicate keys are not allowed; each key must be unique.
🧩 Nesting: Dictionaries can contain other dictionaries as values.
🔍 Lookup Efficiency: Ideal for key-based access and manipulation of data.
Dictionaries are widely used in data modeling, configuration files, JSON-like data structures, and storing structured information.
1. Create a Dictionary
>>> student = {'name': 'Mary', 'id': '8776', 'major': 'CS'}
>>> student
Answer: {'name': 'Mary', 'id': '8776', 'major': 'CS'}
>>> type(student)
Answer: <type 'dict'>
📝 Explanation: A dictionary is created with keys such as 'name', 'id', and 'major'. Each key is mapped to a corresponding value.
2. Get Length of Dictionary
>>> len(student)
Answer: 3
📝 Explanation: The len() function returns the number of key-value pairs in the dictionary.
3. Access a Value by Key
>>> student['name']
Answer: 'Mary'
📝 Explanation: Using the key 'name', we can retrieve its associated value.
4. Add New Key-Value Pair
>>> student['gender'] = 'female'
>>> student
Answer: {'name': 'Mary', 'id': '8776', 'major': 'CS', 'gender': 'female'}
📝 Explanation: We add a new key 'gender' to the dictionary with the value 'female'.
5. Get All Items (Key-Value Pairs)
>>> student.items()
Answer: [('name', 'Mary'), ('id', '8776'), ('major', 'CS'), ('gender', 'female')]
📝 Explanation: The items() method returns all key-value pairs as a list of tuples.
6. Get All Keys
>>> student.keys()
Answer: ['name', 'id', 'major', 'gender']
📝 Explanation: Returns a list of all keys in the dictionary.
7. Get All Values
>>> student.values()
Answer: ['Mary', '8776', 'CS', 'female']
📝 Explanation: Returns a list of all values stored in the dictionary.
8. Nested Dictionaries
>>> student1 = {'name': 'David', 'id': '9876', 'major': 'ECE'}
>>> students = {'1': student, '2': student1}
>>> students
Answer:
{'1': {'name': 'Mary', 'id': '8776', 'major': 'CS', 'gender': 'female'},
'2': {'name': 'David', 'id': '9876', 'major': 'ECE'}}
📝 Explanation: Dictionaries can contain other dictionaries, making them suitable for structured data models (e.g., student records).
9. Check if Dictionary Has a Key
'name' in student
Answer: True
'grade' in student
Answer: False
📝 Explanation:
The in operator checks whether a specific key exists in the dictionary.
👉 Note: has_key() was used in Python 2 and is deprecated in Python 3.
📢 If you found this guide useful, share it with fellow Python learners, follow for more coding tips, and leave a comment with any questions! 🐍💬
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