Viaducta Documentation

Appearance

Python script ​

The Python script component runs your Python code for every record that reaches it. The host embeds CPython (3.11 or newer, 3.12 by default), so you use the Python language and the packages you know.

What you write ​

Connect the input and output first, then open the editor. The template is generated from the connections:

python
def execute(metaData: FlowMetaData, inputData: Customer):
    outputData = CustomerDto()
    services.Next(metaData, outputData)

Customer is the type of the input connection and CustomerDto the type of the output connection. Every type of the flow is a Python class with the same property names (inputData.Email). base64, datetime, uuid and the viaducta package are already imported.

How it runs ​

  • The script runs once when the flow starts. Module-level code runs then, and module-level variables keep their values between records.
  • For every record the component calls execute(metaData, inputData).
  • Each component handles one record at a time, so module state needs no locks.

Sending records on ​

services.Next(metaData, obj) sends a record to the components connected to Output. Call it once, several times or not at all. obj is an instance of a flow class: CustomerDto().

Values ​

Flow typeIn Python
ListA list-like object: index, len(), in, iteration, append, extend, del
Datedatetime.datetime
Decimalfloat; assign a decimal.Decimal to keep full precision

Flow services ​

services has the same members as Services in C#, with the same names. See Flow services.

python
api_url = services.Settings.Get("Crm", "ApiUrl")
services.Log.Information("Calling " + api_url)
services.Messaging.UpdateStatusMessage("Last: " + inputData.Email)

print writes to the host's console. Use services.Log or services.Messaging to see output in Viaducta.

Packages ​

Add pip packages in the flow properties: References → Add → Python package (pip). They are installed into the host's Python.

Your own editor ​

The designer's Python editor highlights syntax. For completion and type checking, install the viaducta package into the Python of your IDE:

bash
pip install viaducta-<version>-py3-none-any.whl

It has type information for services and everything it returns. The host doesn't need it.

Debugger ​

Start the flow with Debug (Ctrl+F5) and set breakpoints in the editor margin. The debugger stops before a line of execute runs and shows its local variables. Step with F10, continue with F5.

Errors ​

An exception that leaves execute goes to the flow's error handling, with your script's traceback and the error line marked in the editor. To report an error and carry on, catch it and call services.HandleExceptionAsync(metaData, inputData, ex).

Example ​

python
import re

def execute(metaData: FlowMetaData, inputData: Customer):
    if not inputData.Email:
        return  # filtered out
    outputData = CustomerDto()
    outputData.Name = inputData.Name.title()
    outputData.Phone = re.sub(r"\D", "", inputData.Phone or "")
    services.Next(metaData, outputData)

Viaducta documentation