Python sketches are not Pythonic

Start by reading the linked Basics/Structure/Redraw/Redraw.py example and the referenced libprocessing issue #150. Compare the current sketch lifecycle with the proposed class-based approach, then clarify which API changes are in scope and how an updated example would demonstrate completion.

Sorry for the vague title, feel free to update it.

Using https://github.com/processing/processing-examples-mewnala/blob/6e416d80852ee9e147b70ae93cbf8f6dda871ba3/Basics/Structure/Redraw/Redraw.py as an example, a mewnala sketch structure and common techniques has several issues that makes it less ideal as Python code:

• Sharing state between frames requires the use of global
• Even when wildcard import is removed, some variables are injected at the runtime and linters catch them as "undefined":
  • https://github.com/processing/libprocessing/issues/150
• setup function is not meaningful, the same results can be achieved just without. Using setup to initialize variables etc. causes even more undefined issues because how scopes work in Python.

As an alternative, a class based approach can solve all these issues:

from mewnala import (
    Line,
    Sketch as BaseSketch,
)

class Sketch(BaseSketch):
    def __init__(self, width=640, height=480):
        super().__init__()

        self.width = width
        self.height = height

    def setup(self):
        self.size = (self.width, self.height)
        self.stroke = 255
        self.loop = False

        self.y = 180

    def draw(self):
        self.background = 0

        self.y -= 4
        if self.y < 0:
            self.y = self.height

        line = Line(0, self.y, self.width, self.y)
        line.draw()

    def mouse_pressed(self):
        self.redraw()


if __name__ == "__main__":
    sketch = Sketch(width=1920, height=1080)
    sketch.run()

No more magic imports, no more undefined variables, and now the sketch has a Python-native syntax feel much more natural comparing to the previous version.

I removed the setter function calls too, it's a Java-native pattern and feels weird with Python.

We can go one step further and eliminate the setup() What does it do for the sketch can be covered by __init__ in a class context.