Python Dictionary Tutorial with Codes and Examples in 2023

Article by: Manish Methani

Last Updated: October 5, 2021 at 10:04am IST
5 min 7 sec read

Python dictionaries are an essential data structure used in programming. They are used to store key-value pairs and provide a fast and efficient way to look up data based on a specific key. In this tutorial, we will cover everything you need to know about Python dictionaries, including how to create, modify, and manipulate them, along with codes and examples.

Step 1: Creating a Python Dictionary

To create a Python dictionary, you can use curly braces and specify key-value pairs separated by colons. Here's an example:

my_dict = {'apple': 1, 'banana': 2, 'cherry': 3}

In this example, we created a dictionary with three key-value pairs: 'apple': 1, 'banana': 2, and 'cherry': 3.

Step 2: Accessing Values in a Python Dictionary

To access the values in a Python dictionary, you can use the keys. Here's an example:

print(my_dict['banana'])

In this example, we accessed the value associated with the 'banana' key in the my_dict dictionary, which is 2.

Step 3: Modifying a Python Dictionary

Python dictionaries are mutable, which means that you can add, delete, and modify key-value pairs. Here's an example:

my_dict['apple'] = 5
my_dict['orange'] = 4
del my_dict['cherry']

In this example, we modified the value associated with the 'apple' key to 5, added a new key-value pair 'orange': 4, and deleted the key-value pair associated with the 'cherry' key.

Step 4: Iterating over a Python Dictionary

To iterate over a Python dictionary, you can use a for loop. Here's an example:

for key, value in my_dict.items():
    print(key, value)

In this example, we used the items() method to access both the keys and values in the my_dict dictionary. The output of this code would be:

apple 5
banana 2
orange 4

Example of Dictionary and how to use it

# Dictionary = key : value

# Create a dictionary
d = {"dog" : "bark", "cat" : "meow" }

# Print the type of the variable
print(type(d))

# Print the contents of the dictionary
print(d)

# Get the entry from a dictionary using the key
print(d["cat"])

# KeyError....snakes is not a key in our dictionary 
print(d["snakes"])

# Check if a dictionary has a given key
print("cat" in d)
print("lion" in d)

# Add an element in a dictionary
d["lion"] = "roar"
print(d)

# Delete an element from a dictionary
del d["lion"]
print(d) 

More about Dictionaries

Given a key, get its value from the dictionary. If the key is not in the dictionary, you can specify the default value as well. In this example, the lion is not in the dictionary so the output will be NA. You can assign a default value if the key is not present in dictionary print(d.get('lion', 'Not in the dictionary'))

# Create a dictionary
d = {"dog" : "bark", "cat" : "meow" }
print(d.get("cat"))
print(d.get("lion"))
print(d.get("lion", "Not in the dictionary"))
print(d.get("lion", "NA"))
print(d.get("dog", "NA")) 

What is Dictionary Comprehension?

Dictionary comprehension is a concise way of creating a new dictionary from an iterable object such as a list, tuple, or set. It is similar to list comprehension, but instead of creating a list, it creates a dictionary.

Dictionary comprehension uses curly braces {} to create a dictionary and a colon : to separate the key-value pairs. The syntax of dictionary comprehension is as follows:

{key: value for item in iterable}

How does Dictionary Comprehension work?

The general idea of dictionary comprehension is to iterate over an iterable object and create a new key-value pair for each item in the iterable. The key and value of each pair can be calculated using an expression or function.

Here is an example of a dictionary comprehension that creates a dictionary of squares:

squares = {x: x*x for x in range(1, 6)}
print(squares)

Output:

{1: 1, 2: 4, 3: 9, 4: 16, 5: 25}

In this example, the iterable object is a range from 1 to 6. The expression x*x calculates the square of each item in the range, and the resulting dictionary has each item in the range as a key and its square as a value.