How do I merge two dictionaries in a single expression in Python
Published: 2024-03-31 11:30:34

[Merging dictionaries in Python](https://pythonkb.com/how-do-i-merge-two-dictionaries-in-a-single-expression-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.

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

devBio.update(tools)

print(devBio)
```

**Output:**

```plaintext
{'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.

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

merged_bio = {**devBio, **tools}

print(merged_bio)
```

**Output:**

```plaintext
{'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.

```python
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.

```python
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.

```python
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 ](https://pythonkb.com/)3.9, the update operator `|=` updates a dictionary with another dictionary's key-value pairs in-place.

```python
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.