# Python

When creating workflows, you'll often need to write dynamic expressions. This page provides an overview of enabling Python expressions and what functions and objects you can use.

## Installing Python

Before we can use Python Expressions, we first need to have Python itself installed.

### Windows

Follow these steps to install Python on Windows.

{% stepper %}
{% step %}
Download the Installer

* Visit the [official Python downloads page](https://www.python.org/downloads/windows/).
* Click on the "Download Windows installer" link for the latest version.
  {% endstep %}

{% step %}
Run the Installer

* Locate the downloaded `.exe` file and double-click to start the installation.
* In the installer window, ensure you check the box labeled "Add Python to PATH."
* Click "Install Now" and follow the on-screen instructions.
  {% endstep %}

{% step %}
Verify the Installation

* Open Command Prompt (`cmd`).
* Type `python --version` and press Enter.
* You should see the Python version number displayed.
  {% endstep %}

{% step %}
Find the Python Installation Path

To locate the Python installation directory on Windows:

* Open Command Prompt.
* Type `where python` and press Enter.
* This command will display the path to the Python executable.

The shared library (`python38.dll`) is typically located in the same directory as the Python executable.

Take note of the full path to the `python38.dll` file. We will need it shortly.
{% endstep %}
{% endstepper %}

### MacOS

Follow these steps to install Python on MacOS.

{% stepper %}
{% step %}
Download the Installer

* Navigate to the [official Python downloads page](https://www.python.org/downloads/macos/).
* Click on the "Download macOS 64-bit installer" link for the latest version.
  {% endstep %}

{% step %}
Run the Installer

* Locate the downloaded `.pkg` file and double-click to start the installation.
* Follow the on-screen instructions to complete the installation.
  {% endstep %}

{% step %}
Verify the Installation

* Open Terminal.
* Type `python3 --version` and press Enter.
* You should see the Python version number displayed.
  {% endstep %}

{% step %}
Find the Python Installation Path

* Open Terminal.
* Type the following command and press Enter:

  ```bash
  which python3
  ```
* This will display the path to the Python executable.

The shared library (`libpython3.8.dylib`) is typically located in the `lib` directory within the Python installation path.

Take note of the full path to the `libpython3.8.dylib` file. We will need it shortly.
{% endstep %}
{% endstepper %}

### Configure Environment Variables

Make sure to configure the `PYTHONNET_PYDLL` environment variable to point to the python DLL found in the previous step.

Also make sure to set `PYTHONNET_RUNTIME` to `coreclr`

{% hint style="info" %}
Refer to the [Pythonnet GitHub project](https://github.com/pythonnet/pythonnet) for detailed documentation.
{% endhint %}

## Installing the Python Feature

The Python Expressions feature is provided by the following package:

```bash
dotnet add package Elsa.Expressions.Python
```

You can enable the feature as follows:

{% code title="Program.cs" %}

```csharp
services.AddElsa(elsa =>
{
   elsa.UsePython();
});
```

{% endcode %}

### Configuration

The `UsePython` extension provides an overload that accepts a delegate that lets you configure the `PythonFeature`, which itself exposes a delegate to configure `PythonOptions`.

For example:

{% code title="Program.cs" %}

```csharp
services.AddElsa(elsa =>
{
   elsa.UsePython(python =>
   {
      python.PythonOptions += options =>
      {
         options.AddScript(sb =>
         {
            sb.AppendLine("def greet():");
            sb.AppendLine("    return \"Hello, welcome to Python!\"");
         });
      }
   });
});
```

{% endcode %}

## Globals

The following functions and objects are available to all Python expressions:

* [output](#output)
* [input](#input)
* [variables](#variables)
* [execution\_context](#execution_context)

### output

The `output` object provides methods to access an activity's output.

```python
# Get the output of the specified activity, optionally specifying a specific output.
get(string, string?): object?

# Gets the output of the last executed activity.
last_result(): object?
```

### input

### variables

The `variables` object provides access to the workflow variables. For example, if your workflow has a variable called OrderId, you can get and set that workflow variable using the following Python expression:

```python
import uuid

# Set the OrderId workflow variable.
variables.OrderId = uuid.uuid4();

# Get the OrderId workflow variable.
orderId = variables.OrderId;

# Set the OrderId workflow variable using the 'set' method.
variables.set("OrderId", uuid.uuid4())

# Get the OrderId workflow variable using the 'get' method.
orderId = variables.get("OrderId")
```

The input object provides access to workflow input.

```python
input.get(string): object?
```

### execution\_context

The execution\_context object provides access to the following information:

```python
workflow_instance_id: string
correlation_id: string
```


---

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Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://docs.elsaworkflows.io/expressions/python.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.