This content originally appeared on DEV Community and was authored by Sabin Sim
Day 10 – Dictionaries
Project: Build a “Student Information System” using Dictionaries
01. Learning Goal
By the end of this lesson, you will be able to:
- Create and manipulate dictionaries (
dict) - Access, update, and delete key-value pairs
- Use dictionary methods like
.keys(),.values(), and.items() - Build nested dictionaries for structured data
02. Problem Scenario
You’re building a simple student record manager.
Each student has attributes like name, age, and major.
Dictionaries allow you to store and retrieve this information efficiently using key-value pairs.
03. Step 1 – What is a Dictionary?
A dictionary stores data as key-value pairs, enclosed in {}.
student = {
"name": "Sabin",
"age": 30,
"major": "Computer Science"
}
Key Features:
- Keys must be immutable (strings, numbers, or tuples).
- Values can be of any data type.
04. Step 2 – Accessing Values
Use keys or .get() to retrieve values safely.
print(student["name"]) # Sabin
print(student["age"]) # 30
# Using get() (avoids KeyError)
print(student.get("major")) # Computer Science
print(student.get("grade")) # None
print(student.get("grade", "N/A")) # Default value if key not found
05. Step 3 – Updating and Adding Data
You can modify existing keys or add new ones dynamically.
student["age"] = 31 # Modify value
student["grade"] = "A" # Add new key
print(student)
06. Step 4 – Removing Data
Use del or .pop() to delete data.
del student["major"] # Remove a specific key
print(student)
grade = student.pop("grade", "N/A") # Remove and return the value
print("Removed:", grade)
07. Step 5 – Dictionary Methods
person = {"name": "Anna", "age": 22}
print(person.keys()) # dict_keys(['name', 'age'])
print(person.values()) # dict_values(['Anna', 22])
print(person.items()) # dict_items([('name', 'Anna'), ('age', 22)])
# Loop through keys and values
for k, v in person.items():
print(k, ":", v)
08. Step 6 – Nested Dictionaries
Dictionaries can contain other dictionaries — useful for structured data.
students = {
"s1": {"name": "Tom", "age": 20},
"s2": {"name": "Anna", "age": 22}
}
print(students["s1"]["name"]) # Tom
09. Step 7 – Practice Examples
Example 1: Print Student Information
student = {"name": "Sabin", "age": 30, "major": "CS"}
for k, v in student.items():
print(f"{k}: {v}")
Example 2: Manage Scores
scores = {"Korean": 90, "English": 85, "Math": 80}
print("Total:", sum(scores.values()))
print("Average:", sum(scores.values()) / len(scores))
10. Step 8 – Mini Project: Student Information System
Create a dictionary-based system that manages and displays student data.
students = {
"101": {"name": "Tom", "age": 20, "grade": "A"},
"102": {"name": "Anna", "age": 22, "grade": "B"},
"103": {"name": "Sabin", "age": 30, "grade": "A+"}
}
for sid, info in students.items():
print(f"ID: {sid}")
for k, v in info.items():
print(f" {k}: {v}")
print()
11. Reflection
You have learned how to:
- Store data efficiently with key-value pairs
- Use dictionary methods to manage and inspect data
- Work with nested dictionaries for complex records
- Build a Student Information System
Next → **Day 11 – Sets
Learn how to handle unique collections and perform set operations.
This content originally appeared on DEV Community and was authored by Sabin Sim
Sabin Sim | Sciencx (2025-10-20T14:30:06+00:00) Python basics – Day 10. Retrieved from https://www.scien.cx/2025/10/20/python-basics-day-10/
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