How to Use Python Dictionary?

Last Updated on October 18, 2023 by Ankit Kochar

Python dictionary is versatile and powerful data structures that play a vital role in every Python programmer’s toolkit. They allow you to store and manipulate data in a way that is both efficient and easy to understand. In this article, we will take a deep dive into the world of Python dictionary, exploring its creation, manipulation, and practical applications. Whether you are a beginner or an experienced Python developer looking to master dictionaries, this guide will equip you with the knowledge and skills you need to make the most out of this essential Python data structure.

Why do we use a Python Dictionary?

A dictionary comes in handy when we have to store or manipulate data and create complex data mappings with its use as a nested data structure with efficient operations. It is helpful in mapping a key to its value that can be accessed in constant time which gives it an edge over the list in terms of searching or retrieving the value for a particular key.

Lets see how to use Python dictionary in detail.

Creating a Python Dictionary

Dictionaries can be created in Python using several ways with the most often used being opening and closing curly braces. We can store values in the dictionary upon its creation where the key and value are separated using a colon (‘:’) with the values being separated by a comma (‘,’). An example can be detailed as:-

Syntax 1 for creating a python dictionary:

languages = {
    "key1": value1, 
    "key2": ,value2
    "key3": value3,
    "key4": value4
  }

Another valid way to create a dictionary is by using the dict() method where the built-in constructor creates a dictionary upon interpreting it.

Syntax 2 for creating a python dictionary:

dict = dict(key1='value1', key2='value2')

Dictionary Comprehension is another but slightly complex way to create a dictionary where an iterator is performed inside to store the key-value pairs in a similar technique to how it is implemented with List Comprehension.

Syntax 3 for creating a python dictionary:

dict = {key: value for key, value in (('key1', 'value1'), ('key2', 'value2'))}

Now that we have a clear idea on how to create a dictionary, we will move forward to study how manipulations can be made on a Python Dictionary.

Accessing a Python Dictionary

Dictionaries in Python can be accessed such that we must provide a key to access the value such as in the given example, a Python Dictionary named languages will have a key named Python, whose value will be printed. In case, the key is not present in dictionary then an error will be thrown:-

Syntax for accessing single value with the given key of python dictionary:

print(languages["Python"])

print(languages.get("Python"))

In case, we want to access all the elements of the dictionary, inclusive of key and value, then the item() method can be called to access the elements. A for loop can be handy in doing so as given given below:-

Syntax for accessing key value pair of python dictionary:

for key, value in languages.items():
  print(f"{key} was created in {value}")

Manipulating Dictionary in Python

Having studied how to create and read a dictionary in python, let’s move onto the techniques we resort to while updating and deleting the keys lying inside the dictionary. To insert a key, we can either place the key inside square brackets with the name of the dictionary and assign the value to it.

Syntax for manipulating the value of given key:

languages[key] = value

Also, we can use the update function to insert a keys with its subsequent values, that can be mentioned as follow:-

languages.update({"Python": 1})

As far as deleting a key from the dictionary is concerned, the operation can be performed with the del or pop method.

Syntax for deleting a key value pair:

languages.pop("Python")
del languages["Python"]

Types of Dictionaries in Python

The power of dictionaries is not limited to these as there are fancy dictionaries that can be imported for their various required use cases. Collection library has various dictionaries like Counter and defaultdict that are used as a tool for problem-solving.

1. Defaultdict

It is a subclass of the general python dictionary and it has a default value for a key in case the key is not found in the dictionary. On creating a defaultdict, we pass the default value, whether we need it to be 0 (int) or an empty list (list). Here is an example with output printed in.

Code for Defaultdict:

from collections import defaultdict
d = defaultdict(int)
d['a'] = 1
d['b'] = 2
print(d['c'])
print(d)

Output:

0
defaultdict(, {'a': 1, 'b': 2, 'c': 0})

2. Counter

It is a special type of dictionary that works as a counter of keys present in the dictionary. It keeps counting the number of elements present in an iterable to store them as a key with their frequency.

Code for Counter:

from collections import Counter
c = Counter([1, 2, 2, 3, 4, 4, 4])
print(c)

Output:

Counter({4: 3, 2: 2, 1: 1, 3: 1})

3. OrderedDict

Another form of dictionary where the order of the elements inserted in the dictionary remains the same. After deleting and reinserting the same element, the element will be positioned in the sequence of insertion. Here is an example code to help the working of OrderedDict better.

Code for OrderedDict:

from collections import OrderedDict
d = OrderedDict()
d['a'] = 1
d['b'] = 2
print(d)

Output:

OrderedDict([('a', 1), ('b', 2)])

4. ChainMap

It is a specialized form of dictionary present in collections library that merges two or more dictionaries into one single dictionary.

Code for ChainMap:

from collections import ChainMap
dict1 = {'a': 1, 'b': 2}
dict2 = {'c': 3, 'd': 4}

chain = ChainMap(dict1, dict2)

print(chain)
print(chain['a'])
print(chain['c'])
print(list(chain.keys()))

Output:

ChainMap({'a': 1, 'b': 2}, {'c': 3, 'd': 4})
1
3
['c', 'd', 'a', 'b']

Conclusion
In conclusion, Python dictionaries are indispensable tools for managing and manipulating data in your Python programs. They offer a flexible and efficient way to store key-value pairs, making them suitable for a wide range of applications. With this comprehensive guide, you’ve learned how to create dictionaries, add and remove elements, access values, and perform various operations to harness the full potential of dictionaries in Python.

As you continue your Python journey, remember that dictionaries are just one of many powerful tools at your disposal. Mastering them will open up new possibilities for your coding projects, allowing you to work with structured data in a way that is both intuitive and efficient. So, go ahead and apply what you’ve learned here, experiment with dictionaries in your code, and watch your Python skills reach new heights.

Frequently Asked Questions Related to Python Dictionary

Here are some FAQs related to Python Dictionary.

1. What is a Python dictionary?
A Python dictionary is an unordered collection of key-value pairs. Each key in a dictionary maps to a specific value, making it easy to retrieve and manipulate data based on these keys. Dictionaries are defined using curly braces {} and can contain various data types as keys and values.

2. How do I create an empty dictionary?
You can create an empty dictionary by using empty curly braces {} or by using the dict() constructor, like this: my_dict = {} or my_dict = dict().

3. Can I have duplicate keys in a dictionary?
No, keys in a dictionary must be unique. If you attempt to add a key that already exists, the new value will overwrite the existing one.

4. How do I access values in a dictionary?
You can access values in a dictionary by using square brackets [] and specifying the key. For example, if you have a dictionary my_dict with a key ‘name’, you can access its value like this: my_dict[‘name’].

5. How can I check if a key exists in a dictionary?
You can use the in keyword to check if a key exists in a dictionary. For example, if ‘key’ in my_dict: will return True if ‘key’ is a key in my_dict.

6. How can I iterate over the keys and values of a dictionary?
You can use a for loop to iterate over the keys, values, or key-value pairs in a dictionary. Use the keys(), values(), or items() methods to access these elements during iteration.

7. Can I nest dictionaries inside other dictionaries?
Yes, you can nest dictionaries inside other dictionaries to create more complex data structures. This allows you to represent hierarchical or structured data in a convenient way.

8. Are dictionaries mutable in Python?
Yes, dictionaries are mutable, which means you can modify their contents by adding, updating, or deleting key-value pairs.

9. What are some common use cases for dictionaries in Python?
Dictionaries are commonly used for tasks such as building configuration settings, counting occurrences of items in a list, storing and retrieving data from databases, and representing JSON-like data structures in Python.

10. Are dictionary operations efficient in terms of time complexity?
Yes, dictionary operations like insertion, retrieval, and deletion are typically very efficient with an average time complexity of O(1), making them suitable for large datasets.