How to Merge Two Dictionaries in Python

Python Dictionary Merge

In Python, dictionaries are a convenient and powerful data structure that allows you to store key-value pairs. There are times when you may need to combine or merge two dictionaries into a single dictionary. In this article, we will explore different ways to merge dictionaries in Python using a single expression.

Method 1: Using the 'update()' method

The easiest and most straightforward way to merge two dictionaries in Python is by using the built-in 'update()' method. This method merges the contents of one dictionary into another by adding or updating the key-value pairs.

            
                x = {'a': 1, 'b': 2}
                y = {'b': 3, 'c': 4}
                z = {}
                
                z.update(x)
                z.update(y)
                
                print(z)

Output:

            
                {'a': 1, 'b': 3, 'c': 4}

In the above code snippet, we first create an empty dictionary z. Then, we use the 'update()' method to merge the contents of dictionaries x and y into z. The result is a merged dictionary z where the values from y overwrite the values from x for the common key 'b'.

Method 2: Using the double asterisk ('**') operator

Another way to merge dictionaries in Python is by using the double asterisk ('**') operator. This operator allows you to pass a dictionary as keyword arguments to a function.

            
                x = {'a': 1, 'b': 2}
                y = {'b': 3, 'c': 4}
                
                z = {**x, **y}
                
                print(z)

Output:

            
                {'a': 1, 'b': 3, 'c': 4}

In this code snippet, we use the double asterisk operator to merge the contents of dictionaries x and y into a new dictionary z. The resulting dictionary z is the same as before, where the values from y overwrite the values from x for the common key 'b'.

Method 3: Using dictionary comprehension

A more advanced and flexible way to merge dictionaries is by using dictionary comprehension. This method allows you to merge multiple dictionaries into a single dictionary in a concise manner.

            
                x = {'a': 1, 'b': 2}
                y = {'b': 3, 'c': 4}
                
                z = {**x, **y, **{'d': 5}}
                
                print(z)

Output:

            
                {'a': 1, 'b': 3, 'c': 4, 'd': 5}

In this code snippet, we use dictionary comprehension with the double asterisk operator to merge the contents of dictionaries x, y, and an additional dictionary with key 'd' and value 5. The resulting dictionary z contains all the key-value pairs from the merged dictionaries.

It is important to note that when merging dictionaries, if a key is present in both dictionaries, the value from the second dictionary will overwrite the value from the first dictionary.

Conclusion

In this article, we have explored different ways to merge dictionaries in Python using a single expression. We have covered the 'update()' method, the double asterisk operator, and dictionary comprehension. Depending on your specific use case, you can choose the most appropriate method for merging dictionaries efficiently and effectively.

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