What Is the Data Structure of Dictionary in Python?


Larry Thompson

A dictionary is a built-in data structure in Python that allows you to store and manipulate collections of key-value pairs. It is also known as a hash table or associative array in other programming languages. In this article, we will explore the data structure of the dictionary in Python and how it can be used effectively.

Dictionary Basics

A dictionary is defined using curly braces ({ }) and consists of comma-separated key-value pairs, where each key is unique within the dictionary. The keys are usually immutable types like strings or numbers, while the values can be of any type.

Let’s consider an example:

my_dict = {'name': 'John', 'age': 25, 'city': 'New York'}

In this example, we have created a dictionary named my_dict with three key-value pairs:

  • ‘name’: ‘John’
  • ‘age’: 25
  • ‘city’: ‘New York’

Accessing Dictionary Elements

To access values in a dictionary, you can use square brackets ([ ]) along with the key name. For example:

print(my_dict['name'])  # Output: John
print(my_dict['age'])   # Output: 25
print(my_dict['city'])  # Output: New York

If a key does not exist in the dictionary, it will raise a KeyError. To avoid this error, you can use the get() method which returns None if the key is not found:

print(my_dict.get('name'))  # Output: John
print(my_dict.get('salary'))  # Output: None

Modifying Dictionary

You can modify the values of a dictionary by assigning a new value to a specific key. For example:

my_dict['age'] = 26
print(my_dict['age'])  # Output: 26

If the key already exists, assigning a new value will update the existing value. If the key does not exist, it will be added to the dictionary with the specified value.

Dictionary Methods

Python provides several built-in methods to perform various operations on dictionaries. Some commonly used methods include:

  • 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 tuples containing key-value pairs.
  • update(): Updates the dictionary with another dictionary or key-value pairs.
  • pop(): Removes and returns the value associated with a given key.

Here is an example that demonstrates some of these methods:

print(my_dict.keys())    # Output: ['name', 'age', 'city']
print(my_dict.values())  # Output: ['John', 26, 'New York']
print(my_dict.items())   # Output: [('name', 'John'), ('age', 26), ('city', 'New York')]

my_dict.update({'salary': 5000})
print(my_dict)           # Output: {'name': 'John', 'age': 26, 'city': 'New York', 'salary': 5000}

print(my_dict)           # Output: {'name': 'John', 'city': 'New York', 'salary': 5000}

These methods provide convenient ways to manipulate and retrieve information from dictionaries.


In this article, we have explored the data structure of the dictionary in Python. We have learned how to define dictionaries, access their elements, modify their values, and use some of the built-in methods available.

Dictionaries are incredibly useful when it comes to organizing and retrieving data based on unique keys. Remember to take advantage of the various methods provided by Python to efficiently work with dictionaries.

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