Dictionaries in Python

Dictionaries are an essential data structure in Python, offering a flexible way to store and manipulate data. They consist of key-value pairs, allowing for efficient data retrieval and manipulation. In this guide, we'll delve into the fundamentals of dictionaries through practical examples and explore various methods to work with them effectively.

Understanding Dictionaries

Let's start with a basic understanding of dictionaries using a common example: types of chai.

chai_types = { "Masala": "Spicy", "Ginger": "Zesty", "Green": "Mild" }

In this dictionary:

• Keys are the types of chai (e.g., "Masala", "Ginger", "Green").

• Values represent the corresponding flavor profiles (e.g., "Spicy", "Zesty", "Mild").

Accessing Values

Accessing values in a dictionary can be done using keys:

print(chai_types["Masala"])  # Output: Spicy
print(chai_types.get("Ginger"))  # Output: Zesty

Handling Missing Keys

When trying to access a key that doesn't exist, KeyError is raised. To avoid this, get() method can be used:

print(chai_types.get("Gingery"))  # Output: None

Modifying and Adding Elements

Dictionaries are mutable, allowing for easy modification:

chai_types["Green"] = "Fresh"

This line updates the value of the "Green" key to "Fresh".

Iterating Through a Dictionary

Iterating over a dictionary provides access to keys:

for type in chai_types:
    print(type)
# Output:
# Masala
# Ginger
# Green

Accessing Keys and Values Simultaneously

To access both keys and values in a loop, use items():

for key, value in chai_types.items():
    print(key, value)
# Output:
# Masala Spicy
# Ginger Zesty
# Green Fresh

Common Operations

Checking for Key Existence

To check if a key exists in a dictionary:

if "Masala" in chai_types:
    print("I have Masala chai") # Output: I have Masala chai

Length of a Dictionary

To get the number of key-value pairs:

print(len(chai_types))  # Output: 3

Removing Elements

You can remove elements using pop() or popitem():

chai_types.pop("Earl Grey")  # Removes and returns the value of "Earl Grey"
chai_types.popitem()  # Removes and returns the last inserted item

Deleting Entire Dictionary or Specific Items

del chai_types['Ginger']  # Removes the key "Ginger" and its value

Copying Dictionaries

To create a copy of a dictionary:

chai_types_copy = chai_types.copy()

Advanced Techniques

Dictionary Comprehension

Using dictionary comprehension to create dictionaries:

squared_num = {x: x**2 for x in range(5)}
print(squared_num)  # Output: {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

Creating Dictionaries with Default Values

keys = ["Masala", "Ginger", "Lemon"]
default_value = "Nice"
new_dict = dict.fromkeys(keys, default_value)
print(new_dict)  # Output: {'Masala': 'Nice', 'Ginger': 'Nice', 'Lemon': 'Nice'}

Will meet you in the next article on Tuples.