Python 3 Ways to merge two dictionaries

Introduction

In Python, dictionaries are a built-in data structure that can store key-value pairs. They are useful for situations where you need to store multiple related values together and retrieve them quickly using a key.

Dictionaries are defined by enclosing the key-value pairs in curly braces {} and separating them with commas. For example, the following code creates a dictionary with three key-value pairs:

x = {'a':1, 'b':2, 'c':3}
y = {'d':4, 'e':5, 'f':6}

In some cases, you may need to merge two dictionaries together. In this article, we will explore three different ways to merge two dictionaries in Python.

Fix 1: Using the Union operator (Python 3.9.0 or greater)

In Python 3.9.0 or greater, a new operator | (Union operator) was introduced. This will allow us to merge two dictionaries easily.

x = {'a':1, 'b':2, 'c':3}
y = {'d':4, 'e':5, 'f':6}
z = x | y
print(z) # {'a':1, 'b':2, 'c':3, 'd':4, 'e':5, 'f':6}

In this example, we use the | operator to merge the two dictionaries x and y. This operator is similar to the | operator used for sets, and it returns a new dictionary containing all the key-value pairs from both dictionaries. If a key is present in both dictionaries, the value from the second dictionary will be used.

It’s important to note that this method is available only in Python 3.9.0 or greater.

Fix 2: Using the double asterisk operator (Python 3.5 or greater)

Another way to merge two dictionaries is by using the ** operator. This operator is used to unpack the contents of a dictionary and pass them as keyword arguments to a function.

x = {'a':1, 'b':2, 'c':3}
y = {'d':4, 'e':5, 'f':6}
z = {**x, **y}
print(z) # {'a':1, 'b':2, 'c':3, 'd':4, 'e':5, 'f':6}

Please note this only works for Python 3.5.0 and above.

Fix 3: Using dict() and items()

Another way to merge two dictionaries is by using the dict() function and the items() method. This method creates a new dictionary and adds the key-value pairs from both dictionaries using the items() method which returns a list of key-value pairs.

x = {'a':1, 'b':2, 'c':3}
y = {'d':4, 'e':5, 'f':6}
z = dict(list(x.items()) + list(y.items()))
print(z) # {'a':1, 'b':2, 'c':3, 'd':4, 'e':5, 'f':6}

In this example, we use the items() method to get a list of key-value pairs from both dictionaries x and y. We then use the + operator to concatenate the lists and pass them to the dict() function to create a new dictionary with the key-value pairs from both dictionaries.

It’s important to note that this method is available in all versions of Python.

Conclusion

In Python, there are multiple ways to merge two dictionaries. Each method has its own advantages and disadvantages.

• The first method, using the | operator, is the most straightforward and efficient way to merge two dictionaries, but it’s only available in Python 3.9.0 or greater.

• The second method, using the ** operator, is a simple and elegant way to merge two dictionaries, but it’s only available in Python 3.5 or greater.

• The third method, using the dict() function and the items() method, is the most versatile and backward-compatible way to merge two dictionaries, as it’s available in all versions of Python.

It’s important to choose the right approach for your specific use case, taking into account the version of Python you are using and the requirements of your project.