How to use defaultdict Python effectively for handling a dictionary?

In order to not get stuck while processing values in a dictionary because of nonexistent values, there is a specific subclass defaultdict Python to handle it.

defaultdict python

Python is one of the most versatile languages out there. It offers a wide range of data structures for its users. One such data structure is the Python defaultdict. The defaultdict Python is the dictionary structure that is a collection of key-value pairs that can be easily searched and manipulated. 

In this article, we will primarily focus on the data structure “defaultdict” and learn how to use it well.

What is defaultdict in Python?

Python defaultdict is one of the in-built subclasses in the dict class. Defaultdict Python behaves like an object that provides a Python dict default value for a nonexistent key. This Python class default value is specified in the constructor of the defaultdict object itself. The Python defaultdict is used whenever we are working with multiple levels of nesting. Defaultdict Python is useful for saving time whenever there is a nonexistent key in the Python default dictionary before the programmer can assign it a value.

What are the benefits of using defaultdict Python?

There are several benefits of using Python defaultdict. Here are some of the most major ones mentioned below:

  • The core benefit of defaultdict Python is that it saves time and improves the readability of code. 
  • Python defaultdict aids in providing a more concise and much more efficient code. Python defaultidict does is removing unnecessary repetitive checks for figuring out whether the key exists or is non-existent. 
  • Python defaultdict provides a Python dict default value to the nonexistent keys in the Python default dictionary making the code much more robust and less prone to errors.

Importance of Defaultdict in Python

Python defaultdict is one of the most important data structures in Python. It is because defaultdict makes the process of working with the Python default dictionary much easier. Python defaultdict reduces the amount of code that is required to perform a specific task. It is the reason Python defaultdict is an essential tool for the Python developer.

Understanding Dictionaries in Python

Before truly understanding what Python defaultdict is, it is important for us to understand the basics of what dictionaries in Python are. Therefore, here we go…

Definition of Dictionaries

The dictionaries in Python are key-value pairs. It is important to understand that these keys are unique, immutable objects, however, the associated values can be of any type. Another important thing to follow would be that dictionaries are defined using curly braces i.e. “{ }”.

Key-Value Pair Concept

The key-value pair is the backbone of the dictionary concept. It retrieves the corresponding value from the dictionary and is an immutable data type. Data types such as strings, numbers, or tuples. Also, the value included in the key-value pair concept can include defaultdict list, tuples, and multiple other objects.

Examples of Dictionaries in Python -

Below is an example of what a dictionary in Python looks like:

My_dictionary = {“Key1”:”Value1”, “Key2”: “Value2”, “Key3”: “Value3”}

The dictionary of Python mentioned above has three key-value pairs. Here the corresponding value for “Key1” is “Value1”, for “Key2” is “Value2”, and for “Key3” is “Value3”.

What is the difference between Defaultdict vs Dictionaries?

The primary difference between defaultdict and a regular dictionary would be that the Python defaultdict automatically creates key-value pairs for nonexistent keys. This happens whenever the key is accessed for the first time. On the contrary, a regular dictionary raises a KeyError exception whenever there is a nonexistent key.

Defaultdict Example -

Below is a defaultdict example in Python, let’s have a look:

From collections import defaultdict

My_Dictionary = defaultdict(int)
My_Dictionary[“Key1”] = 1
My_Dictionary[“Key2”] = 2

In the example above, we have created a Python defaultdict that uses the int constructor. This int constructor is used as the default factory function. The moment we try to access the keys “Key1” and “Key2”, the code will generate the corresponding values that are 1 and 1. However, if we try to access the key “Key3”, which doesn’t exist within the dictionary, the defaultdict Python automatically creates a key-value with the default value of 0.

How does defaultdict work?

Below are the steps to defaultdict Python, have a look:

1. Importing Defaultdict

Before we can use Python defaultdict in our code, we need to import it from the collections module. Below is the code to that:

from collections import defaultdict

2. Initializing Defaultdict

To initialize defaultdict Python, we have to specify a default factory function that returns a Python dict default value for any nonexistent key. Here's an example:

My_Dictionary = defaultdict (lambda: “default value”)

In the example above, we have created a Python defaultdict that makes use of lambda function. It will act as a default factory function. This lambda function will return the string “default value” for any of the nonexistent keys.

Examples of Using Defaultdict -

Here are some examples of using defaultdict Python, have a look:
The code below is for counting elements in the list
From collections import defaultdict

Fruit_list =[“Apple”, ”Orange, ”Kiwi”, ”Banana”,” Watermelon”, ”Lemon”]
my_list= defaultdict(int)
For item in my_Fruit_list:
My_list[item] += 1

The code below is for grouping elements in a list:

Fruit_list =[“Apple”, ”Orange, ”Kiwi”, ”Banana”,” Watermelon”, ”Lemon”]
My_list = defaultdict (list)
For item in Fruit_list:

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A lot of companies use Python for mobile app development. It is because it has a multitude of functions similar to defaultdict. Defaultdict Python is a dictionary-like object. It is key to the development process because when we start to develop on a large scale, making and seeing changes again & again because of nonexistent values is difficult. Defaultdict Python allows the developer to run the code even if the values are nonexistent and streamlines the development process to achieve results faster.

General FAQ

  • Is it possible to use defaultdict with custom classes as default factory functions?
  • Is there any performance difference between defaultdict and a regular dictionary?
  • Can we modify the default factory function once the defaultdict has been created?
  • Is it possible to use defaultdict with other data structures other than dictionaries?
Aparna <span>Growth Strategist</span>
Written By
Aparna Growth Strategist

Aparna is a growth specialist with handsful knowledge in business development. She values marketing as key a driver for sales, keeping up with the latest in the Mobile App industry. Her getting things done attitude makes her a magnet for the trickiest of tasks. In free times, which are few and far between, you can catch up with her at a game of Fussball.

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