Python Learning Session-08: Dictionaries in Python – Key-Value Magic!

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👋 Welcome Back!

We’ve explored lists, which are great for storing ordered collections. But what if you need to store data with labels? For example, a student’s name and their marks. Lists can do it, but it’s messy. Enter Dictionaries—Python’s way of storing data as key-value pairs.

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✅ What is a Dictionary?

A dictionary is like a real-life dictionary: you look up a word (key) and get its meaning (value). In Python:

• Keys are unique
• Values can be anything (numbers, strings, lists, even another dictionary)
• Defined using curly braces {}

Example:

Python

student = {

"name": "Alice",

"age": 21,

"marks": 85

}

print(student)

Output:

{'name': 'Alice', 'age': 21, 'marks': 85}

✔ Why useful? Perfect for structured data like user profiles, product details, etc.

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✅ Creating Dictionaries

Python

# Empty dictionary

my_dict = {}

# Dictionary with data

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✅ Accessing Values

Use the key:

Python

print(student["name"]) # Alice

✔ Pro Tip: If you use a key that doesn’t exist, Python throws an error. Use get() to avoid that:

Python

print(student.get("grade", "Not Available"))

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✅ Adding & Updating Data

Python

student["grade"] = "A" # Add new key-value

student["marks"] = 90 # Update existing value

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✅ Removing Data

• pop() → Remove by key

Python

student.pop("age")

• clear() → Remove all items

Python

student.clear()

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✅ Looping Through Dictionaries

Python

for key, value in student.items():

print(key, ":", value)

✔ Real-world example: Displaying user details in a profile page.

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✅ Dictionary Methods You’ll Love

• keys() → All keys
• values() → All values
• items() → All key-value pairs

Example:

Python

print(student.keys())

print(student.values())

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✅ Nested Dictionaries

Dictionaries inside dictionaries:

Python

students = {

"101": {"name": "Alice", "marks": 85},

"102": {"name": "Bob", "marks": 78}

}

print(students["101"]["name"]) # Alice

✔ Why powerful? Great for storing complex data like JSON.

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✅ Summary

Dictionaries are the backbone of Python data handling. They’re fast, flexible, and perfect for real-world applications like APIs, databases, and configurations.

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🔥 Challenge for You

Create a dictionary of 5 countries and their capitals. Then:

• Print all keys and values
• Add a new country
• Remove one country

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👉 Next Session: Session-09: Tuples in Python – Immutable Collections!