Introduction

What is SimpleScratchExtension?

SimpleScratchExtension is a python framework to help writing scratch HTTP extension. The goals are:

• Hide http protocol
• Focus work on write just components business code

The main class of the framework is scratch.extension.Extension. Extension use components from scratch.components that represent scratch extension blocks. To build an extension you should just extend Extension class and implement do_init_components() that should return the components list. The http service for scratch communication is provided by scratch.extension.ExtensionService object that take an extension and service http requests.

Code Structure

Tests

First Example: set sprite position

A simple example is the simplest way to explain the framework philosophy. The complete (and runnable) code is first.py but now we will focus our attentions on the key parts:

1. Extension class
2. Component creation
3. Interact with components
4. Service start
5. Description file saving

In this extension we create a single value reporter block (AKA sensor: the round blocks) and use set() component's method to change the sensor value. We will create a new scratch extension that contain just one block named position and the user can change position's value by our python component.

Extension class

Extension an abstract class is what you should implement if you want create your own extension. The only method that you must implement to make it concrete is do_init_components() where you can create your own components and return as list (or iterator in general). In this case you need just a component and you can use specialized Sensor component (reporters without arguments):

def do_init_components(self):
    self.component = Sensor.create(self, name="position")
    return [self.component]

Now we can change sensor's value simply by ex.component.set(new_val) or hide it by delegating set method in a more readable change_position() extension method:

def change_position(self, position):
    self.component.set(position)

Your extension call doesn't need nothing else. You can

1. instantiate it extension=MyFirstScratchExtension()
2. create service by es=ExtensionService(extension)
3. save json extension descriptor by save_service_description() helper
4. start service by es.start()

NOw you can import extension descriptor in Scratch:

Open Scratch, hold shift and click File menu:

• Chose Import experimental HTTP Extension
• Browse to where you saved json extension descriptor and select it
• Build: When "green flag" clicked, forever set x to position where position is a gray sensor in More Blocks

Now your sprite will be set in x position that you set by change_position() extension's method.

Future directions

Licence