Python sketches are not Pythonic

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.

首先阅读链接的 Basics/Structure/Redraw/Redraw.py 示例以及引用的 libprocessing issue #150。将当前的 sketch 生命周期与提议的基于类的方法进行比较，然后明确哪些 API 更改属于范围之内，以及更新后的示例将如何展示完成情况。