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Python | Merging two Dictionaries

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  • Difficulty Level : Basic
  • Last Updated : 08 Aug, 2022
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There are various ways in which Dictionaries can be merged by the use of various functions and constructors in Python. In this article, we will discuss a few ways of merging dictionaries. 

Using the method update() 

By using the method update() in Python, one list can be merged into another. But in this, the second list is merged into the first list and no new list is created. It returns None

Example: 

Python3




# Python code to merge dict using update() method
def Merge(dict1, dict2):
    return(dict2.update(dict1))
 
 
# Driver code
dict1 = {'a': 10, 'b': 8}
dict2 = {'d': 6, 'c': 4}
 
# This return None
print(Merge(dict1, dict2))
 
# changes made in dict2
print(dict2)

Output:

None
{'c': 4, 'a': 10, 'b': 8, 'd': 6}

Using ** in Python 
 

This is generally considered a trick in Python where a single expression is used to merge two dictionaries and stored in a third dictionary. The single expression is **. This does not affect the other two dictionaries. ** implies that an argument is a dictionary. Using ** [double star] is a shortcut that allows you to pass multiple arguments to a function directly using a dictionary. For more information refer **kwargs in Python. Using this we first pass all the elements of the first dictionary into the third one and then pass the second dictionary into the third. This will replace the duplicate keys of the first dictionary. 
 

Example: 

Python3




# Python code to merge dict using a single
# expression
def Merge(dict1, dict2):
    res = {**dict1, **dict2}
    return res
     
# Driver code
dict1 = {'a': 10, 'b': 8}
dict2 = {'d': 6, 'c': 4}
dict3 = Merge(dict1, dict2)
print(dict3)

Output

{'a': 10, 'b': 8, 'd': 6, 'c': 4}

Using | in Python 3.9

In the latest update of python now we can use “|” operator to merge two dictionaries. It is a very convenient method to merge dictionaries.

Example:

Python3




# code
# Python code to merge dict using a single 
# expression
def Merge(dict1, dict2):
    res = dict1 | dict2
    return res
       
# Driver code
dict1 = {'x': 10, 'y': 8}
dict2 = {'a': 6, 'b': 4}
dict3 = Merge(dict1, dict2)
print(dict3)
 
# This code is contributed by virentanti16

Output:

{'x': 10, 'a': 6,  'b': 4, 'y': 8}

Using for loop and keys() method

Python3




# code
# Python code to merge dictionary
def Merge(dict1, dict2):
    for i in dict2.keys():
        dict1[i]=dict2[i]
    return dict1
     
# Driver code
dict1 = {'x': 10, 'y': 8}
dict2 = {'a': 6, 'b': 4}
dict3 = Merge(dict1, dict2)
print(dict3)
 
# This code is contributed by Bhavya Koganti

Output

{'x': 10, 'y': 8, 'a': 6, 'b': 4}

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