Skencil User's Guide: Introduction

User Scripting | User Scripting | The Example Scripts

## Introduction

### Safe and Advanced Scripts

As mentioned above user scripts in Skencil can cause data loss. To make things easier for you in this regard, Skencil supports two kinds of user scripts, safe scripts and advanced scripts.

Safe scripts take care of undo handling for you and they restrict what your script can actually do to keep you from harm. The disadvantage of this approach is that you can't do everything you might want to do with a safe script.

The advanced script has no restrictions but it has to take care of undo handling itself, which isn't difficult but has to be done with care.

### The Script Function

Regardless of whether a script is a safe script or an advanced script it is just a Python function that accepts a context object as parameter. The context is an instance with three attributes:

`document`

  The document for which the script was called.

  The document contains all objects that make up the drawing and it manages the selection.

`application`

  The application object.

  The application object has methods for setting and retrieving the application's clipboard and to pop-up message boxes and file dialogs.

`main_window`

  The top-level window containing the canvas widget that shows the current drawing. It has methods for loading and saving documents, among others.

A simple 'hello world' type script might look like this:

    def hello_world(context):
        context.application.MessageBox(title = "My Script",
                                       message = "Hello World!")

### Registering Scripts

The Script menu just shows all the scripts in the script registry, so to have a script appear in that menu, you have to put it into the registry.

The registry is managed in a subpackage `Scripting` of the toplevel package `Sketch` (The name of the package is a leftover from the time Skencil was called `Sketch', in case you're wondering). The function needed here is `AddFunction` and is called like this:

`AddFunction(name, title, function)`

`name`

  is a name for that script. This name should be unique, as the scripts are identified in the registry by this name. It doesn't have to be the same as the function name.

`title`

  The text of the menu entry.

`function`

  the function that implements the script, e.g. `hello_world` above.

There are a few optional keyword arguments, one of which is type. The value of script_type must be either `SafeScript` (the default) or `AdvancedScript`. Both values are defined in the `Scripting` subpackage. The registry functions are covered in more detail in the script registry section.

As an example, registering the hello world script might look like this:

    import Sketch.Scripting
    Sketch.Scripting.AddFunction("hello_world", "Hello World", hello_world)

First we import the package `Sketch.Scripting` and then we call the `AddFunction` function.

For more information about the organization of Skencil's code have a look at the API overview.

### The Startup Script

The only thing left to do is to get some user supplied code to run on startup, so it can define and register scripts. To do that just create a file `userhooks.py` in the directory `~/.sketch/`. If such a file exists it is automatically executed when Skencil starts. More precisely, the directory `~/.sketch/` is inserted at the front of Python's modules search path and a module `userhooks.py` is imported.

You can put arbitrary code in there not just scripts, but one way to implement and register our `hello_world` script would be a `userhooks.py` file like this:

    # example for ~/.sketch/userhooks.py

    def hello_world(context):
        context.application.MessageBox(title = "My Script",
                                       message = "Hello World!")

    # register script
    import Sketch.Scripting
    Sketch.Scripting.AddFunction("hello_world", "Hello World", hello_world)

User Scripting | User Scripting | The Example Scripts