Topic 14: Dictionary Data Type in Python

In Python, a dictionary is one of the most powerful and flexible data types. It allows you to store data in key–value pairs, just like a real-world dictionary where words (keys) have meanings (values). Dictionaries are unordered, mutable, and indexed by unique keys, making them ideal for quick lookups and data organization.

Syntax of Dictionary

# Creating a dictionary
my_dict = {
    "name": "Alice",
    "age": 25,
    "city": "Delhi"
}

Keys: Must be unique and immutable (e.g., strings, numbers, tuples).
Values: Can be of any data type (string, list, number, etc.).

Creating a Dictionary

1️⃣ Using Curly Braces `{}`

student = {"name": "John", "roll_no": 101, "course": "B.Tech"}

2️⃣ Using `dict()` Constructor

student = dict(name="John", roll_no=101, course="B.Tech")

Accessing Dictionary Elements

You can access values using their key names.

student = {"name": "John", "roll_no": 101, "course": "B.Tech"}
print(student["name"])      # Output: John
print(student.get("course"))  # Output: B.Tech

Adding and Updating Elements

student["city"] = "Meerut"     # Add new key-value pair
student["course"] = "M.Tech"   # Update existing value
print(student)

Removing Elements

student.pop("roll_no")     # Removes a specific key
student.popitem()          # Removes the last inserted item
del student["name"]        # Deletes a key-value pair
student.clear()            # Clears entire dictionary

Common Dictionary Functions

Function	Description	Example
`len()`	Returns the number of items	`len(student)`
`keys()`	Returns all keys	`student.keys()`
`values()`	Returns all values	`student.values()`
`items()`	Returns all key-value pairs	`student.items()`
`update()`	Updates with another dictionary	`student.update({"marks": 90})`
`copy()`	Returns a shallow copy	`new_dict = student.copy()`

Looping Through Dictionary

student = {"name": "John", "marks": 90, "grade": "A"}

# Loop through keys
for key in student:
    print(key, ":", student[key])

Output:

name : John  
marks : 90  
grade : A

Flowchart: Working of Dictionary

Dictionary data type

 Example Program

# Dictionary Example Program
employee = {
    "name": "Rahul",
    "department": "IT",
    "salary": 50000
}

print("Employee Name:", employee["name"])
employee["salary"] = 55000
employee["location"] = "Mumbai"

print("Updated Employee Record:", employee)

Output:

Employee Name: Rahul  
Updated Employee Record: {'name': 'Rahul', 'department': 'IT', 'salary': 55000, 'location': 'Mumbai'}

Advantages of Dictionary

Fast lookups and modifications
Flexible data storage
Easy to merge and manipulate
Ideal for real-world mapping (like student details, employee data, etc.)

Conclusion

Python dictionaries are an essential part of Python programming. They help store, organize, and access data efficiently using key-value pairs. Once you master dictionaries, you can handle complex data and structures in Python easily!

Python Programming for Everyone