How do I merge two dictionaries in a single expression in Python

Merging dictionaries in Python is a common operation that can be accomplished in various ways. This functionality is particularly useful when you want to combine data stored in two or more dictionaries into a single dictionary. Let's go through the methods mentioned, with simple examples for each.

1. Using the `update()` Method

The update() method adds elements from one dictionary to another. If there are overlapping keys, the values from the second dictionary will overwrite those from the first.

devBio = {"name": "Ihechikara", "age": 500, "language": "Python"}
tools = {"dev environment": "JupyterLab", "os": "Windows", "visualization": "Matplotlib"}

devBio.update(tools)

print(devBio)

Output:

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

2. Using the Double Asterisk Operator (**)

The double asterisk operator allows you to unpack dictionary items, enabling the merging of two or more dictionaries in a single expression.

devBio = {"name": "Ihechikara", "age": 500, "language": "Python"}
tools = {"dev environment": "JupyterLab", "os": "Windows", "visualization": "Matplotlib"}

merged_bio = {**devBio, **tools}

print(merged_bio)

Output:

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

3. Using the `chain()` Method

The chain() method from the itertools module is used for treating consecutive sequences as a single sequence. While not directly merging dictionaries, it can be used alongside dict() to combine dictionaries.

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)

4. Using the `ChainMap()` Method

ChainMap() from the collections module creates a single view of multiple dictionaries. You can convert it back to a dictionary to merge them.

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)

5. Using the Merge Operator (|)

Introduced in Python 3.9, the merge operator | provides a succinct syntax to merge two dictionaries.

devBio = {"name": "Ihechikara", "age": 500, "language": "Python"}
tools = {"dev environment": "JupyterLab", "os": "Windows", "visualization": "Matplotlib"}

merged_bio = devBio | tools

print(merged_bio)

6. Using the Update Operator (|=)

Also introduced in Python 3.9, the update operator |= updates a dictionary with another dictionary's key-value pairs in-place.

devBio = {"name": "Ihechikara", "age": 500, "language": "Python"}
tools = {"dev environment": "JupyterLab", "os": "Windows", "visualization": "Matplotlib"}

devBio |= tools

print(devBio)

Summary:

The update() method and the |= operator modify the original dictionary.
The ** operator, chain() method, ChainMap() method, and the | operator create a new dictionary without altering the originals.
The | and |= operators are the most concise but require Python 3.9 or later.
The ** operator is widely used for its simplicity and readability, working in Python 3.5 and later.