Python

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🔹 1. What is a Dictionary?

A dictionary is a collection of key–value pairs.

Example structure:

key : value

Example:

name : Sameer
age : 25
city : Hyderabad

In Python dictionaries are written using curly brackets {}.

✔ Stores data as key : value
✔ Ordered (Python 3.7+)
✔ Changeable (mutable)
✔ No duplicate keys

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🔹 2. Creating a Dictionary

Example 1

student = {
    "name": "Sameer",
    "age": 22,
    "city": "Hyderabad"
}print(student)

Output

{'name': 'Sameer', 'age': 22, 'city': 'Hyderabad'}

📌 Explanation

• "name", "age", "city" → keys
• "Sameer", 22, "Hyderabad" → values

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🔹 3. Accessing Dictionary Values

Use the key name to access values.

Example 2

student = {
    "name": "Ayesha",
    "age": 21,
    "city": "Warangal"
}print(student["name"])
print(student["age"])

Output

Ayesha
21

📌 Explanation
The value is retrieved using the key.

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🔹 4. Changing Dictionary Values

Example 3

student = {
    "name": "Saddam",
    "age": 24
}student["age"] = 25print(student)

Output

{'name': 'Saddam', 'age': 25}

📌 Explanation
Dictionaries are mutable, so values can be updated.

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🔹 5. Adding New Key–Value Pairs

Example 4

student = {
    "name": "Chandini",
    "age": 23
}student["city"] = "Hyderabad"print(student)

Output

{'name': 'Chandini', 'age': 23, 'city': 'Hyderabad'}

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🔹 6. Removing Items from Dictionary

Example 5

student = {
    "name": "Gousya",
    "age": 22,
    "city": "Warangal"
}student.pop("city")print(student)

Output

{'name': 'Gousya', 'age': 22}

📌 Explanation
pop() removes a key-value pair.

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🔹 7. Dictionary Length

Example 6

student = {
    "name": "Sameer",
    "age": 22,
    "city": "Hyderabad"
}print(len(student))

Output

3

📌 Explanation
len() counts the number of keys.

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🔹 8. Loop Through Dictionary

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Example 7: Loop Through Keys

student = {
    "name": "Sameer",
    "age": 22,
    "city": "Hyderabad"
}for key in student:
    print(key)

Output

name
age
city

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Example 8: Loop Through Values

student = {
    "name": "Ayesha",
    "age": 21,
    "city": "Warangal"
}for value in student.values():
    print(value)

Output

Ayesha
21
Warangal

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Example 9: Loop Through Key–Value Pairs

student = {
    "name": "Saddam",
    "age": 24,
    "city": "Hyderabad"
}for key, value in student.items():
    print(key, ":", value)

Output

name : Saddam
age : 24
city : Hyderabad

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🔹 9. Checking if Key Exists

Example 10

student = {
    "name": "Sameer",
    "age": 22
}print("name" in student)
print("city" in student)

Output

True
False

📌 Explanation
Checks if a key exists in dictionary.

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🔹 10. Nested Dictionary

A dictionary inside another dictionary.

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Example 11

students = {
    "student1": {
        "name": "Sameer",
        "age": 22
    },
    "student2": {
        "name": "Ayesha",
        "age": 21
    }
}print(students["student1"]["name"])

Output

Sameer

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🔹 11. Real-Life Example

Employee Information

employee = {
    "name": "Gousya",
    "salary": 30000,
    "department": "IT"
}print("Employee Name:", employee["name"])
print("Salary:", employee["salary"])
print("Department:", employee["department"])

Output

Employee Name: Gousya
Salary: 30000
Department: IT

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🔹 12. Common Dictionary Methods

Method	Purpose
keys()	Returns keys
values()	Returns values
items()	Returns key-value pairs
pop()	Removes item
update()	Updates dictionary