Python Dictionaries

Dictionaries in Python are mutable, unordered collections that store key-value pairs. Each key in a dictionary must be unique, and the keys are used to access the associated values. Here’s a comprehensive guide to working with dictionaries in Python:

Creating Dictionaries

You can create dictionaries using curly braces {} with key-value pairs separated by colons.

# Creating an empty dictionary

empty_dict = {}

# Creating a dictionary with some key-value pairs

student = {

    "name": "John Doe",

    "age": 20,

    "courses": ["Math", "Computer Science"]

}

Accessing Values

You can access values in a dictionary by using their keys.

# Accessing values by key

print(student["name"])  # Output: John Doe

print(student["age"])   # Output: 20

print(student["courses"])  # Output: ['Math', 'Computer Science']

Modifying Dictionaries

You can modify the values associated with a specific key, add new key-value pairs, and delete existing ones.

Changing Values

# Changing the value associated with a key

 student["age"] = 21

 print(student["age"])  # Output: 21

 

Adding Key-Value Pairs

# Adding a new key-value pair

student["grade"] = "A"

print(student)  # Output: {'name': 'John Doe', 'age': 21, 'courses': ['Math', 'Computer Science'], 'grade': 'A'}

Removing Key-Value Pairs

# Removing a key-value pair using del

del student["grade"]

print(student)  # Output: {'name': 'John Doe', 'age': 21, 'courses': ['Math', 'Computer Science']}

# Removing a key-value pair using pop()

age = student.pop("age")

print(age)      # Output: 21

print(student)  # Output: {'name': 'John Doe', 'courses': ['Math', 'Computer Science']}

Dictionary Methods

Dictionaries come with several built-in methods.

keys(), values(), and items()

These methods are used to access the keys, values, and key-value pairs in the dictionary.

print(student.keys())   # Output: dict_keys(['name', 'courses'])

print(student.values()) # Output: dict_values(['John Doe', ['Math', 'Computer Science']])

print(student.items())  # Output: dict_items([('name', 'John Doe'), ('courses', ['Math', 'Computer Science'])])

update()

This method updates the dictionary with key-value pairs from another dictionary or from an iterable of key-value pairs.

# Updating a dictionary with another dictionary

student.update({"age": 21, "grade": "A"})

print(student)  # Output: {'name': 'John Doe', 'courses': ['Math', 'Computer Science'], 'age': 21, 'grade': 'A'}

# Updating a dictionary with an iterable of key-value pairs

student.update([("age", 22), ("grade", "B")])

print(student)  # Output: {'name': 'John Doe', 'courses': ['Math', 'Computer Science'], 'age': 22, 'grade': 'B'}

get()

This method returns the value for a specified key if the key is in the dictionary, otherwise it returns a default value.

print(student.get("name"))       # Output: John Doe

print(student.get("grade"))      # Output: B

print(student.get("address", "Not Available"))  # Output: Not Available

popitem()

This method removes and returns the last inserted key-value pair as a tuple.

last_item = student.popitem()

print(last_item)  # Output: ('grade', 'B')

print(student)    # Output: {'name': 'John Doe', 'courses': ['Math', 'Computer Science'], 'age': 22}

clear()

This method removes all items from the dictionary.

student.clear()

print(student)  # Output: {}

 

Summary

• Creating Dictionaries: Use curly braces {} with key-value pairs separated by colons.
• Accessing Values: Use keys to access values.
• Modifying Dictionaries: Add, change, and remove key-value pairs.
• Dictionary Methods: Use methods like keys(), values(), items(), update(), get(), popitem(), and clear().
• Iterating Over Dictionaries: Iterate over keys, values, and key-value pairs.

Dictionaries are highly versatile and useful for various applications, including data representation, counting, and simple databases. Mastering dictionaries will greatly enhance your ability to work with structured data in Python.