A bare-bone Thonny AutoPep8 extension.

autopep8.py

import autopep8
from thonny import get_workbench
from tkinter.messagebox import showinfo

DEBUG = False

# Save to:
# %APPDATA%\Roaming\Thonny\plugins\Python3.10\site-packages\thonnycontrib\autopep8.py

# references:
# https://bitbucket.org/aivarannamaa/tktextext/src/master/tktextext.py
# https://github.com/hhatto/autopep8?tab=readme-ov-file#use-as-a-module
# https://github.com/thonny/thonny/blob/master/thonny/editors.py
# https://github.com/thonny/thonny/blob/master/thonny/codeview.py
# https://github.com/thonny/thonny/blob/master/thonny/plugins/cells.py


def run_autopep8_on_code():
    workbench = get_workbench()
    editor = workbench.get_editor_notebook().get_current_editor()

    # thonny.CodeView
    view = editor.get_code_view()
    # thonny.CodeViewText, tktextext.EnhancedText, thonny.SyntaxText,
    cvtext = editor.get_text_widget()
    curpos = list(cvtext.get_cursor_position())  # [line, col]

    if DEBUG:
        filename = editor.get_filename()
        msg = f"workbench={str(workbench)} editor={str(editor)} file={str(filename)}\nclass={editor.__class__.__name__}" \
            f"\ncursor_position={curpos}"
        showinfo(title="Debug", message=msg)

        # text = cvtext.get("1.0", "end")
        # msg="text={text}"
        # showinfo(title="Pos", message=msg)

        # tktextext.TweakableText
        # widget.set_content("something")

    code = view.get_content()
    fixed_code = autopep8.fix_code(code, options={'aggressive': 2})
    if code != fixed_code:
        view.set_content(fixed_code, keep_undo=True)
        editor.select_line(*curpos)
        # cvtext.tag_remove("sel", "1.0", 'end') # tk.END='end'
        view._clean_selection()


def load_plugin():
    get_workbench().add_command(command_id="autopep8",
                                menu_name="tools",
                                command_label="AutoPep8",
                                handler=run_autopep8_on_code,
                                default_sequence="<Control-Shift-KeyPress-F>"
                                )