Dictionaries in Python

Module - 4 Data Structures in Python

Lesson - 6 Dictionaries in Python

Overview

Dictionaries in Python are a capable and adaptable data structure that permits you to store and manipulate collections of key-value pairs. In this lesson, we'll cover the essentials of dictionaries in Python, including how to create and access dictionaries, include and remove elements, and perform common operations.

Dictionaries in Python-min.png

Introduction to Dictionary

"In Python, dictionaries are represented by curly braces ({}) encasing a comma-separated list of key-value pairs, where each key is separated from its corresponding value by a colon (: )." In Python, a dictionary could be a collection of key-value pairs, where each key is one of a kind and related to a particular value. An industry example to explain a dictionary in Python is in the customer relationship management (CRM) software industry. In CRM software, customer information is stored and managed using dictionaries. For instance, let's say that a CRM software company has a dictionary containing customer information for a particular client. The Dictionary may look something like this:

customer_info = {
    "Name": "John Smith",
    "Age": 35,
    "Email": "johnsmith@example.com",
    "Phone": "555-123-4567",
    "Address": "123 Main Street",
    "City": "Anytown",
    "State": "CA",
    "Zip": "12345"
}

In this example, the Dictionary contains various customer information, such as name, age, email, phone, address, city, state, and zip code. The keys in the Dictionary (e.g., "Title", "Age", "Email", etc.) correspond to the type of data being put away, and the values (e.g., "John Smith", 35, "johnsmith@example.com", etc.) are the genuine information points.

Within the CRM computer program industry, dictionaries are valuable since they permit customer information to be stored and recovered rapidly and effectively. The software can rapidly look for and recover the required data by utilizing unique keys to distinguish each piece of data.

Creating and Accessing Dictionaries

Python creates a dictionary using curly braces {} and key-value pairs separated by colons. For example:


# Creating a dictionary of ages 
ages = {"Alice": 28, "Bob": 35, "Charlie": 42} 
# Creating an empty dictionary 
empty_dict = {}

To access an element in a dictionary, you can use square brackets [] and the element's key. For example:


# Accessing the age of Alice 
alice_age = ages["Alice"] 
print(alice_age)

If the key does not exist in the Dictionary, you will get a KeyError. To avoid this, you can use the get() method, which returns None if the key does not exist:


# Using the get() method 
bob_age = ages.get("Bob") 
print(bob_age)  
# Using a default value with get() 
david_age = ages.get("David", 0) 
print(david_age)

Adding, Updating and Removing Elements

To add a new key-value pair to a dictionary, you can use square brackets [] and assign a value to the new key:

# Adding a new element to the dictionary 
ages["David"] = 21

To update an existing element, you can use the same syntax:


# Updating an element in the dictionary 
ages["Bob"] = 36

To remove an element from a dictionary, you can use the del keyword or the pop() method:


# Removing an element with del 
del ages["Charlie"] 
# Removing an element with pop() 
alice_age = ages.pop("Alice")

Common Operations

Dictionaries in Python have many useful methods and operations. Here are a few examples:

keys(): returns a list of all the keys in the Dictionary
values(): returns a list of all the values in the Dictionary
items(): returns a list of all the key-value pairs in the Dictionary as tuples
Len(): returns the number of elements in the Dictionary
in keyword: checks if a key exists in the Dictionary

Here's an example of how to use some of these operations:

# Printing all the keys 
print(ages.keys()) 

# Printing all the values
print(ages.values()) 

# Printing all the key-value pairs
print(ages.items()) 

# Printing the number of elements 
print(len(ages)) 

# Checking if a key exists 
if "David" in ages: 
    print("David's age is", ages["David"])
else: 
    print("David is not in the dictionary")

Few things to keep in mind while making a dictionary

Keys must be unique: A dictionary in Python must have unique keys. If you attempt to include a key that already exists within the Dictionary, the unused value will overwrite the old value.
Keys must be immutable: Keys in a Python dictionary must be permanent, suggesting they cannot be changed once made. This is often because word references utilize the hash value of the keys for efficient lookup, and mutable keys can cause hash collisions.
Values can be of any type: Values in a Python dictionary can be of any type, including strings, numbers, lists, tuples, and even other dictionaries.
Making a dictionary: You'll be able to make a dictionary in Python using curly braces {} or the dict() constructor. On utilizing the dict() constructor, you can pass in key-value pairs as positional arguments, otherwise, you can pass in a list of tuples containing the key-value pairs.
Accessing values: You'll get to the value associated with a key in a dictionary using square brackets []. You will use the get() method, which returns None if the key isn't found, or a default value if provided. In case the key does not exist within the Dictionary, a KeyError will be raised.
Altering a dictionary: You can include, update, or erase key-value pairs using square brackets []. To include a new key-value pair, essentially allot a value to a new key. To overhaul an existing key-value pair, assign a new value to the existing key. To delete a key-value pair, utilize the del keyword.
Iterating over a dictionary: You'll iterate over the keys or values of a dictionary utilizing the keys(), values(), or items() methods. The keys() method returns a see of the Dictionary's keys, the values() method returns a view of the Dictionary's values, and the items() method returns a see of the Dictionary's key-value pairs.

Conclusion

Dictionaries in Python are flexible and effective data structures that can be utilized for a wide assortment of applications. They permit you to store and manipulate collections of key-value pairs and give numerous valuable methods and operations for working with those collections. Whether you're working with huge datasets or little scripts, dictionaries are a basic tool in any Python programmer's toolkit.

Key Takeaways

Dictionaries in Python are collections of key-value pairs created using curly braces {} and key-value pairs separated by colons.
Keys must be unique and immutable, while values can be of any type.
To access elements, square brackets [] are used with the element's key, and the get() method can be used to avoid KeyError.
Elements can be added, updated, or removed using square brackets [], the del keyword, or the pop() method.
Common operations on dictionaries include keys(), values(), items(), len(), and the in keyword.
When creating a dictionary, it is important to remember the uniqueness and immutability of keys and the ability of values to be of any type.

Quiz

Which of the following is a true statement about Python dictionaries?
1. Dictionaries can only store key-value pairs of the same data type.
2. Keys in a dictionary can be changed after they are created.
3. Dictionaries are created using square brackets [].
4. Keys in a dictionary must be unique and immutable.

Answer: d. Keys in a dictionary must be unique and immutable.