1. Creating a Dictionary

Dictionaries are created using curly braces {} with key-value pairs separated by colons : and items separated by commas.

Syntax:

my_dict = {key1: value1, key2: value2, key3: value3, ...}

Example:

person = {"name": "John", "age": 30, "city": "New York"}
print(person)

Output:

{'name': 'John', 'age': 30, 'city': 'New York'}

Real-world Example:

Dodagatta Nihar creates a dictionary to store information about his favorite books:

favorite_books = {"title": "The Alchemist", "author": "Paulo Coelho", "year": 1988}
print(favorite_books)

Output:

{'title': 'The Alchemist', 'author': 'Paulo Coelho', 'year': 1988}

---

2. Accessing Dictionary Values

You can access the value associated with a specific key by using square brackets [] or the get() method.

Syntax:

value = my_dict[key]

Example:

person = {"name": "John", "age": 30, "city": "New York"}
print(person["age"])

Output:

30

Real-world Example:

Harsha accesses the year of publication for a book:

book_info = {"title": "1984", "author": "George Orwell", "year": 1949}
print(book_info["year"])

Output:

1949

---

3. Adding and Updating Items

You can add new key-value pairs or update existing ones using square brackets [].

Syntax:

my_dict[key] = value

Example:

person = {"name": "John", "age": 30}
person["city"] = "New York"  # Adding a new key-value pair
person["age"] = 31           # Updating an existing value
print(person)

Output:

{'name': 'John', 'age': 31, 'city': 'New York'}

Real-world Example:

Vasanta Kumar updates his contact information:

contact_info = {"email": "vasanta@example.com", "phone": "123-456-7890"}
contact_info["phone"] = "987-654-3210"  # Updating phone number
contact_info["address"] = "123 Elm St"  # Adding address
print(contact_info)

Output:

{'email': 'vasanta@example.com', 'phone': '987-654-3210', 'address': '123 Elm St'}

---

4. Removing Items

You can remove items using the del statement, the pop() method, or the popitem() method.

Using del:

Removes a key-value pair by key.

person = {"name": "John", "age": 30, "city": "New York"}
del person["city"]
print(person)

Output:

{'name': 'John', 'age': 30}

Using pop():

Removes and returns the value for the specified key.

person = {"name": "John", "age": 30, "city": "New York"}
age = person.pop("age")
print(person)
print(f"Removed age: {age}")

Output:

{'name': 'John', 'city': 'New York'}
Removed age: 30

Using popitem():

Removes and returns the last key-value pair as a tuple.

person = {"name": "John", "age": 30, "city": "New York"}
last_item = person.popitem()
print(person)
print(f"Removed item: {last_item}")

Output:

{'name': 'John', 'age': 30}
Removed item: ('city', 'New York')

Real-world Example:

Praveen removes an entry from his inventory:

inventory = {"item1": 50, "item2": 100, "item3": 200}
removed_item = inventory.pop("item2")
print(inventory)
print(f"Removed item2 quantity: {removed_item}")

Output:

{'item1': 50, 'item3': 200}
Removed item2 quantity: 100

---

5. Looping Through a Dictionary

You can loop through dictionaries using loops to access keys, values, or key-value pairs.

Looping through keys:

person = {"name": "John", "age": 30, "city": "New York"}
for key in person:
    print(key)

Output:

name
age
city

Looping through values:

person = {"name": "John", "age": 30, "city": "New York"}
for value in person.values():
    print(value)

Output:

John
30
New York

Looping through key-value pairs:

person = {"name": "John", "age": 30, "city": "New York"}
for key, value in person.items():
    print(f"{key}: {value}")

Output:

name: John
age: 30
city: New York

Real-world Example:

Dodagatta Nihar prints details of his favorite authors:

authors = {"Paulo Coelho": "The Alchemist", "George Orwell": "1984", "J.K. Rowling": "Harry Potter"}
for author, book in authors.items():
    print(f"Author: {author}, Book: {book}")

Output:

Author: Paulo Coelho, Book: The Alchemist
Author: George Orwell, Book: 1984
Author: J.K. Rowling, Book: Harry Potter

---

6. Dictionary Methods

Dictionaries have several built-in methods, including copy(), clear(), get(), and update().

Using copy():

Returns a shallow copy of the dictionary.

person = {"name": "John", "age": 30}
copy_person = person.copy()
print(copy_person)

Output:

{'name': 'John', 'age': 30}

Using clear():

Removes all items from the dictionary.

person = {"name": "John", "age": 30}
person.clear()
print(person)

Output:

{}

Using get():

Returns the value for the specified key if it exists, or a default value if it doesn’t.

person = {"name": "John", "age": 30}
print(person.get("name"))
print(person.get("city", "Unknown"))

Output:

John
Unknown

Using update():

Updates the dictionary with elements from another dictionary or from an iterable of key-value pairs.

person = {"name": "John", "age": 30}
person.update({"city": "New York", "job": "Engineer"})
print(person)

Output:

{'name': 'John', 'age': 30, 'city': 'New York', 'job': 'Engineer'}

Real-world Example:

Harsha updates his contact details:

contact_info = {"email": "harsha@example.com", "phone": "123-456-7890"}
contact_info.update({"phone": "098-765-4321", "address": "456 Elm St"})
print(contact_info)

Output:

{'email': 'harsha@example.com', 'phone': '098-765-4321', 'address': '456 Elm St'}

---

Few more examples

Example 1: Creating and Accessing a Dictionary

student = {"name": "Alice", "age": 22, "major": "Computer Science"}
print(student["name"])

Output:

Alice

Example 2: Adding and Removing Items

student = {"name": "Alice", "age": 22}
student["graduated"] = True
del student["age"]
print(student)

Output:

{'name': 'Alice', 'gradu

ated': True}

Example 3: Looping Through a Dictionary

student = {"name": "Alice", "age": 22, "major": "Computer Science"}
for key, value in student.items():
    print(f"{key}: {value}")

Output:

name: Alice
age: 22
major: Computer Science

---