Python Merge Dictionaries – Merging Two Dicts in Python

Dictionaries are one of the built-in data structures in Python. You can use them to store data in key-value pairs.

You can read about the different methods you can use to access, modify, add, and remove elements in a dictionary here.

In this article, you'll learn how to merge two dictionaries using the following:

• The update() method.
• The double asterisk/star operator (**).
• The chain() method.
• The ChainMap() method.
• The merge operator (|).
• The update operator (|=).

How to Merge Two Dictionaries in Python

In this section, we'll discuss the different methods you can use to merge dictionaries in Python, along with code examples.

All the examples you'll see in this article will involve the merging of two dictionaries, but you can merge as many as you want.

How to Merge Two Dictionaries in Python Using the update() Method

The update() method is a built-in method that you can use to add data to dictionaries.

Consider the dictionary below:

devBio = {
  "name": "Ihechikara",
  "age": 500,
  "language": "Python"
}

devBio.update({"role": "Technical Writer"})

print(devBio)
# {'name': 'Ihechikara', 'age': 500, 'language': 'Python', 'role': 'Technical Writer'}

In the code above, we created a dictionary called devBio with three key and value pairs: {'name': 'Ihechikara', 'age': 50, 'language': 'Python'}.

Using the update() method, we added another key and value pair: devBio.update({"role": "Technical Writer"}).

In the same manner, we can merge two dictionaries by passing another dictionary as a parameter to the update() method. Here's an example:

devBio = {
  "name": "Ihechikara",
  "age": 500,
  "language": "Python"
}

tools = {
  "dev environment": "JupyterLab",
  "os": "Windows",
  "visualization": "Matplotlib"
}

devBio.update(tools)

print(devBio)
# {'name': 'Ihechikara', 'age': 500, 'language': 'Python', 'dev environment': 'JupyterLab', 'os': 'Windows', 'visualization': 'Matplotlib'}

In the code above, we created two dictionaries — devBio and tools.

Using the update() method, we merged the key and value pairs of the tools dictionary to the devBio dictionary: devBio.update(tools).

The merged dictionaries looked like this:

{
    'name': 'Ihechikara', 
    'age': 500, 
    'language': 'Python', 
    'dev environment': 'JupyterLab', 
    'os': 'Windows', 
    'visualization': 'Matplotlib'
}

How to Merge Two Dictionaries in Python Using the Double Asterisk Operator (**)

You can use the double asterisk (also called double star) operator (**) to "unpack" and merge the key and value pairs of two or more dictionaries into a variable.

Here's a code example:

devBio = {
  "name": "Ihechikara",
  "age": 500,
  "language": "Python"
}

tools = {
  "dev environment": "JupyterLab",
  "os": "Windows",
  "visualization": "Matplotlib"
}

merged_bio = { **devBio, **tools}

print(merged_bio)
# {'name': 'Ihechikara', 'age': 500, 'language': 'Python', 'dev environment': 'JupyterLab', 'os': 'Windows', 'visualization': 'Matplotlib'}

In the code above, we unpacked the devBio and tools dictionaries using the double asterisk operator: { **devBio, **tools}.

We then stored them in a variable called merged_bio.

How to Merge Two Dictionaries in Python Using the chain() Method

The chain() method takes multiple iterable objects as its parameter. It merges and returns the objects as one iterable object.

You have to import the chain() method from the itertools module before using it:

from itertools import chain

devBio = {
  "name": "Ihechikara",
  "age": 500,
  "language": "Python"
}

tools = {
  "dev environment": "JupyterLab",
  "os": "Windows",
  "visualization": "Matplotlib"
}

merged_bio = dict(chain(devBio.items(), tools.items()))

print(merged_bio)
# {'name': 'Ihechikara', 'age': 500, 'language': 'Python', 'dev environment': 'JupyterLab', 'os': 'Windows', 'visualization': 'Matplotlib'}

In the code above, we passed the dictionaries to be merged as parameters to the chain() method: chain(devBio.items(), tools.items()).

We used the items() method to access the key and value pairs of each dictionary.

Lastly, we nested the chain() method and its parameters in the dict() method: dict(chain(devBio.items(), tools.items())).

The dict() method can be used to create a dictionary so we used it to convert the iterable objects returned (the key and value pairs) into a dictionary, and stored them in the merged_bio variable.

How to Merge Two Dictionaries in Python Using the ChainMap() Method

The ChainMap() method works the same way as the chain() method as regards to merging dictionaries. The main difference is that you don't need the items() method to access the key and value pairs of the dictionaries.

You can import the ChainMap() method from the collections module.

Here's how you can use the ChainMap() method to merger two dictionaries:

from collections import ChainMap

devBio = {
  "name": "Ihechikara",
  "age": 500,
  "language": "Python"
}

tools = {
  "dev environment": "JupyterLab",
  "os": "Windows",
  "visualization": "Matplotlib"
}

merged_bio = dict(ChainMap(devBio, tools))

print(merged_bio)
# {'name': 'Ihechikara', 'age': 500, 'language': 'Python', 'dev environment': 'JupyterLab', 'os': 'Windows', 'visualization': 'Matplotlib'}

You can check the explanation in the last section to understand the logic in the code above.

How to Merge Two Dictionaries in Python Using the Merge Operator (|)

The merge operator (|) was first introduced in Python 3.9. It's a shorter and simpler syntax that you can use to merge dictionaries.

Here's an example:

from collections import ChainMap

devBio = {
  "name": "Ihechikara",
  "age": 500,
  "language": "Python"
}

tools = {
  "dev environment": "JupyterLab",
  "os": "Windows",
  "visualization": "Matplotlib"
}

merged_bio = devBio | tools

print(merged_bio)
# {'name': 'Ihechikara', 'age': 500, 'language': 'Python', 'dev environment': 'JupyterLab', 'os': 'Windows', 'visualization': 'Matplotlib'}

So to merge the devBio and tools dictionary, we put the | operator between them:  devBio | tools.

How to Merge Two Dictionaries in Python Using the Update Operator (|=)

The update operator (|=) operator is another operator that was introduced in Python 3.9.

It works just like the update() method. That is:

from collections import ChainMap

devBio = {
  "name": "Ihechikara",
  "age": 500,
  "language": "Python"
}

tools = {
  "dev environment": "JupyterLab",
  "os": "Windows",
  "visualization": "Matplotlib"
}

devBio |= tools

print(devBio)
# {'name': 'Ihechikara', 'age': 50, 'language': 'Python', 'dev environment': 'JupyterLab', 'os': 'Windows', 'visualization': 'Matplotlib'}

In the code above, we used the |= to mege the key and value pairs in the tools dictionary into the devBio dictionary.

Summary

In this article, we talked about dictionaries in Python. You can use them to store data in key-value pairs.

We saw how to merge two dictionaries in Python using:

• The update() method.
• The double asterisk/star operator (**).
• The chain() method.
• The ChainMap() method.
• The merge operator (|).
• The update operator (|=).

Each method had its own section with code examples that showed how to use them to merge dictionaries.

Happy coding! You can learn more about Python on my blog.