Dictionaries Introduction0%
Dictionaries Introduction
Beginner9 min read•Updated: 2026-09-03
Dictionaries Introduction
Dictionaries store data in key-value pairs, offering near-instantaneous lookups by key.
Key Concepts & Detailed Explanation
Dictionary anatomy:
- Key-Value structure: { key1: val1, key2: val2 }
- Unique keys: Keys must be unique and hashable (strings, numbers, tuples).
- Mutable: Values can be updated, inserted, or removed.
- Ordered: Since Python 3.7, dictionaries maintain insertion order.
Code Examples & Output
Python
# Creating a student dictionary
student = {
"roll_no": 101,
"name": "Arun Kumar",
"course": "Python for Beginners",
"fee_paid": True,
"score": 92.5
}
print("Student dict:", student)
print("Student name:", student["name"])
print("Total keys:", len(student))
Expected Output:
Output
Student dict: {'roll_no': 101, 'name': 'Arun Kumar', 'course': 'Python for Beginners', 'fee_paid': True, 'score': 92.5}
Student name: Arun Kumar
Total keys: 5
Best Practices & Common Pitfalls
Always use immutable types (like strings or integers) as dictionary keys. Never use lists.
Practice Quiz
1. Can a list be used as a dictionary key in Python?
- A) Yes, anytime
- B) No, because lists are mutable and unhashable
- C) Only if it contains integers
- D) Only in Python 3
Answer: B
Explanation: Dictionary keys must be hashable; lists are unhashable.
2. Do Python dictionaries maintain insertion order in modern Python 3.7+?
- A) No, dictionaries are always completely random
- B) Yes, insertion order is guaranteed
- C) Only when sorted
- D) Only with collections.OrderedDict
Answer: B
Explanation: Insertion order preservation is guaranteed in Python 3.7+.
Practice Challenge
Create a dictionary describing a computer lab with keys for lab_name, computers_count, and has_projector.
Next Lesson
Accessing & Updating Items
Continue learning with hands-on practice, examples, and exercises in the upcoming topic.
Related Lessons
| Previous Lesson | Next Lesson |
|---|---|
| Nested Sets | Accessing & Updating Items |
Practice Quiz
Test your understanding of this lesson with 1 questions. Each question has one correct answer.