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