How to Add Values to Dictionary in Python

Last Updated : 23 Jan, 2025

The task of adding values to a dictionary in Python involves inserting new key-value pairs or modifying existing ones. A dictionary stores data in key-value pairs, where each key must be unique. Adding values allows us to expand or update the dictionary's contents, enabling dynamic manipulation of data.

For example, if we start with a dictionary a = {0: 'Carrot', 1: 'Raddish'}, we can add a new key-value pair like a[2] = 'Brinjal', resulting in the dictionary {0: 'Carrot', 1: 'Raddish', 2: 'Brinjal'}.

Using union operator

union operator (|) is a efficient way to add values by merging dictionaries as it creates a new dictionary with the combined key-value pairs, leaving the original dictionaries unchanged.

Python

a = {0: 'Carrot', 1: 'Raddish'} b = {2: 'Brinjal', 3: 'Potato'} res = a | b print(res)

Output

{0: 'Carrot', 1: 'Raddish', 2: 'Brinjal', 3: 'Potato'}

Explanation: a | b combines all key-value pairs from a and b, with values from b overwriting those in a if duplicate keys exist .

Table of Content

Using unpacking

** unpacking syntax expands dictionaries into key-value pairs ,making it a clean and effective way to merge dictionaries into a new one .

Python

a = {0: 'Carrot', 1: 'Raddish'} b = {2: 'Brinjal', 3: 'Potato'} res = {**a, **b} print(res)

Output

{0: 'Carrot', 1: 'Raddish', 2: 'Brinjal', 3: 'Potato'}

Explanation: {**a, **b} merges dictionaries by unpacking all key-value pairs from a and b, with values from b overwriting those in a if duplicate keys exist.

Using update()

update() method allows us to add multiple key-value pairs from another dictionary or an iterable of key-value pairs to an existing dictionary. If a key exists, its value will be updated.

Python

a = {0: 'Carrot', 1: 'Raddish'} b = {2: 'Brinjal', 3: 'Potato'}  res = a.copy()  #  creates a shallow copy of dictionary `a` res.update(b) print(res)

Output

{0: 'Carrot', 1: 'Raddish', 2: 'Brinjal', 3: 'Potato'}

Explanation: res.update(b) merges b into res by adding all key-value pairs, updating existing keys in res if duplicates exist, and appending new keys from b .

Using dictionary comprehension

This method iterates over key-value pairs from one or more dictionaries and constructs a new dictionary. While less efficient, it is useful when we need to apply logic while adding values.

Python

a = {0: 'Carrot', 1: 'Raddish'} b = {2: 'Brinjal', 3: 'Potato'}  res = {k: v for d in (a, b) for k, v in d.items()} print(res)

Output

{0: 'Carrot', 1: 'Raddish', 2: 'Brinjal', 3: 'Potato'}

Explanation: dictionary comprehension merges a and b by iterating over both dictionaries and collecting key-value pairs into a new dictionary.

Using assignment operator

This is the simplest way to add a single key-value pair to a dictionary. If the key already exists, its value will be updated.

Python

a = {0: 'Carrot', 1: 'Raddish'} # Adding a single key-value pair a[2] = 'Brinjal' print(a)

Output

{0: 'Carrot', 1: 'Raddish', 2: 'Brinjal'}

Explanation: a[2] = 'Brinjal' adds key 2 with the value 'Brinjal' to dictionary a.

Add new keys to a dictionary in Python

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