ASSIGNMENT
ASSIGNMENT
Q.6 How to create Dictionary in Python? Discuss various methods with example.
Answer :-
- A dictionary in Python is an unordered, mutable, and indexed collection used to store data in the form of key-value pairs.
- Each key in a dictionary must be unique and immutable (e.g., strings, numbers, or tuples), while values can be of any type and can repeat.
Syntax of a Dictionary
- A dictionary is defined using curly braces {} with key-value pairs separated by colons
my_dict = {key1: value1, key2: value2, …}
Creating a Dictionary
Using Curly Braces {}
my_dict = {“name”: “Alice”, “age”: 25, “city”: “New York”}
print(my_dict)
# Output: {‘name’: ‘Alice’, ‘age’: 25, ‘city’: ‘New York’}
Using the dict()
my_dict = dict(name=”Alice”, age=25, city=”New York”)
print(my_dict)
# Output: {‘name’: ‘Alice’, ‘age’: 25, ‘city’: ‘New York’}
From a List of Tuples
my_dict = dict([(“name”, “Alice”), (“age”, 25), (“city”, “New York”)])
print(my_dict)
# Output: {‘name’: ‘Alice’, ‘age’: 25, ‘city’: ‘New York’}
Using Dictionary Comprehension
my_dict = {x: x**2 for x in range(1, 4)}
print(my_dict)
# Output: {1: 1, 2: 4, 3: 9}
Dictionary Methods
Python provides several built-in methods for performing operations on dictionaries. Below are the most common methods with examples:
keys()
Purpose: Returns a view object of all the keys in the dictionary.
Example:
my_dict = {“name”: “Alice”, “age”: 25}
print(my_dict.keys())
# Output: dict_keys([‘name’, ‘age’])
values()
Purpose: Returns a view object of all the values in the dictionary.
Example:-
my_dict = {“name”: “Alice”, “age”: 25}
print(my_dict.values())
# Output: dict_values([‘Alice’, 25])
items()
Purpose: Returns a view object of all key-value pairs as tuples.
Example:-
my_dict = {“name”: “Alice”, “age”: 25}
print(my_dict.items())
# Output: dict_items([(‘name’, ‘Alice’), (‘age’, 25)])
get()
Purpose: Returns the value of the specified key. If the key does not exist, it returns None (or a specified default value).
Example:-
my_dict = {“name”: “Alice”, “age”: 25}
print(my_dict.get(“name”)) # Output: Alice
print(my_dict.get(“city”, “Not Found”)) # Output: Not Found
update()
Purpose: Updates the dictionary with key-value pairs from another dictionary or iterable.
Example :-
my_dict = {“name”: “Alice”, “age”: 25}
my_dict.update({“city”: “New York”, “age”: 26})
print(my_dict)
# Output: {‘name’: ‘Alice’, ‘age’: 26, ‘city’: ‘New York’}
pop()
Purpose: Removes the specified key and returns its value. Raises a KeyError if the key does not exist.
Example :-
my_dict = {“name”: “Alice”, “age”: 25}
age = my_dict.pop(“age”)
print(age) # Output: 25
print(my_dict) # Output: {‘name’: ‘Alice’}
popitem()
Purpose: Removes and returns the last inserted key-value pair as a tuple.
Example :-
my_dict = {“name”: “Alice”, “age”: 25}
item = my_dict.popitem()
print(item) # Output: (‘age’, 25)
print(my_dict) # Output: {‘name’: ‘Alice’}
clear()
Purpose: Removes all items from the dictionary.
Example :-
my_dict = {“name”: “Alice”, “age”: 25}
my_dict.clear()
print(my_dict) # Output: {}
copy()
Purpose: Returns a shallow copy of the dictionary.
Example :-
my_dict = {“name”: “Alice”, “age”: 25}
copied_dict = my_dict.copy()
print(copied_dict)
# Output: {‘name’: ‘Alice’, ‘age’: 25}
setdefault()
Purpose: Returns the value of the specified key. If the key does not exist, it inserts the key with a specified default value.
Example :-
my_dict = {“name”: “Alice”}
city = my_dict.setdefault(“city”, “Unknown”)
print(city) # Output: Unknown
print(my_dict) # Output: {‘name’: ‘Alice’, ‘city’: ‘Unknown’}
Example of Dictionary
# Create a dictionary
student = {“name”: “John”, “age”: 20, “course”: “Computer Science”}# Access keys, values, and items
print(student.keys()) # dict_keys([‘name’, ‘age’, ‘course’])
print(student.values()) # dict_values([‘John’, 20, ‘Computer Science’])
print(student.items()) # dict_items([(‘name’, ‘John’), (‘age’, 20), (‘course’, ‘Computer Science’)])# Update dictionary
student.update({“age”: 21, “grade”: “A”})
print(student)
# {‘name’: ‘John’, ‘age’: 21, ‘course’: ‘Computer Science’, ‘grade’: ‘A’}# Remove an item
removed = student.pop(“course”)
print(removed) # Output: Computer Science
print(student)
# {‘name’: ‘John’, ‘age’: 21, ‘grade’: ‘A’}