How to concatenate 3 dictionaries in python

When it is required to concatenate two dictionaries into a single entity, the ‘update’ method can be used.

Table of Contents Show

Explanation
How do you combine 3 dictionaries?
How do you combine multiple dictionaries into one in Python?
How do I add multiple dictionaries to a list in Python?
Is concatenation possible in dictionary Python?

A dictionary is a ‘key-value’ pair.

Below is a demonstration for the same −

Example

Live Demo

my_dict_1 = {'J':12,'W':22}
my_dict_2 = {'M':67}
print("The first dictionary is :")
print(my_dict_1)
print("The second dictionary is :")
print(my_dict_2)
my_dict_1.update(my_dict_2)
print("The concatenated dictionary is :")
print(my_dict_1)

Output

The first dictionary is :
{'J': 12, 'W': 22}
The second dictionary is :
{'M': 67}
The concatenated dictionary is :
{'J': 12, 'W': 22, 'M': 67}

Explanation

Two dictionaries are defined, and are displayed on the console.

The ‘update’ method is called on the first dictionary by passing second dictionary as parameter.
This would help concatenate the dictionary.
This is displayed on the console.

Updated on 12-Mar-2021 12:44:07

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This is a Python Program to concatenate two dictionaries into one dictionary.

Problem Description

The program takes two dictionaries and concatenates them into one dictionary.

Problem Solution

1. Declare and initialize two dictionaries with some key-value pairs
2. Use the update() function to add the key-value pair from the second dictionary to the first dictionary.
3. Print the final dictionary.
4. Exit.

Program/Source Code

Here is source code of the Python Program to add a key-value pair to a dictionary. The program output is also shown below.

d1={'A':1,'B':2}
d2={'C':3}
d1.update(d2)
print("Concatenated dictionary is:")
print(d1)

Program Explanation

1. User must enter declare and initialize two dictionaries with a few key-value pairs and store it in separate variables.
2. The update() function is used to add the key-value pair from the second to the first dictionary.
3. The final updated dictionary is printed.

Runtime Test Cases

 
Case 1:
Concatenated dictionary is:
{'A': 1, 'C': 3, 'B': 2}

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Sometimes, while working with dictionaries, we might have a problem in which we have lists as it’s value and wish to have it cumulatively in single list by concatenation. This problem can occur in web development domain. Let’s discuss certain ways in which this task can be performed.

Method #1 : Using sum() + values() This is the most recommended method and one liner to perform this task. In this, we access all list values using values() and concatenation utility is performed using sum().

Python3

test_dict = {"Gfg" : [4, 5], "is" : [6, 8], "best" : [10]}

print("The original dictionary is : " + str(test_dict))

res = sum(test_dict.values(), [])

print("The Concatenated list values are : " + str(res))

Output :

The original dictionary is : {'Gfg': [4, 5], 'best': [10], 'is': [6, 8]}
The Concatenated list values are : [4, 5, 10, 6, 8]

Method #2 : Using chain() + * operator This task can also be performed using the combination of these methods. In these, we just use inbuilt function of chain for concatenation to list and * operator is used to access all the list values into one.

Python3

from itertools import chain

test_dict = {"Gfg" : [4, 5], "is" : [6, 8], "best" : [10]}

print("The original dictionary is : " + str(test_dict))

res = list(chain(*test_dict.values()))

print("The Concatenated list values are : " + str(res))

Output :

The original dictionary is : {'Gfg': [4, 5], 'best': [10], 'is': [6, 8]}
The Concatenated list values are : [4, 5, 10, 6, 8]

Method #3 : Using extend(),list() and values() methods

Python3

test_dict = {"Gfg" : [4, 5], "is" : [6, 8], "best" : [10]}

print("The original dictionary is : " + str(test_dict))

x=[]

for i in list(test_dict.values()):

x.extend(i)

print("The Concatenated list values are : " + str(x))

Output

The original dictionary is : {'Gfg': [4, 5], 'is': [6, 8], 'best': [10]}
The Concatenated list values are : [4, 5, 6, 8, 10]

How do you combine 3 dictionaries?

How to Merge Dictionaries in Python?.

1) Using update() method..

2) Using merge(|) operator..

3) Using ** operator..

4) Unpacking the second dictionary..

5) Using collection.ChainMap() method..

6) Using itertools. chain().

7) Using dictionary comprehension..

8) Add values of common keys..

How do you combine multiple dictionaries into one in Python?

Python 3.9 has introduced the merge operator (|) in the dict class. Using the merge operator, we can combine dictionaries in a single line of code. We can also merge the dictionaries in-place by using the update operator (|=).

How do I add multiple dictionaries to a list in Python?

Since Python 3.9, it is possible to merge two dictionaries with the | operator. If they have the same key, it is overwritten by the value on the right. You can combine multiple dictionaries. Like += for + , |= for | is also provided.

Is concatenation possible in dictionary Python?

Python concatenate dictionaries with same keys The counter holds the data in an unordered collection just like a hashable object. To concatenate the dictionary, I have used dictionary = dictionary1 + dictionary2. To get the output, I have used print(“dictionary”, str(dictionary)).