Waiting for heavy functions question

[philipbergwerf]

What happens if there is a python error inside the render() function because I did not fix all bugs?

A simple solution for this is to call instead a new function render_no_error() that cannot raise an exception. This function would call render()

def render_no_error():
    try:
        render()
    except Exception as e:
        pass  # handle the exception the way you want

The drawback of this technique is to silently suppress exceptions, which makes debugging hard. You will need to leave a trace of the exceptions somewhere, perhaps on stderr or better in a log file or perhaps display it in a tkinter window. You could also catch specific exception types before the Exception type.

it is becoming annoying because it does this drawing every time you press a key

I have been using for a long time a Python program to write mathematical documents. I type in an editor and a subprocess parses what I type and calls other programs to create a Pdf file. I see two windows: the editor and the pdf viewer. The event that triggers the recalculation ot the pdf file is not every keystroke. Instead I recalculate the pdf file every time I type Ctrl-S in the editor to save the source file. This is a very fluid workflow. I suggest that you bind a sequence such as Ctrl-S to the Text or the root widget that would simultaneously save your work and redraw the canvas. It allows you to type as many characters as you want without triggering a redraw.

I'm not a very good tkinter programmer because I don't use it very often but I can imagine solutions to your idea of hiding the canvas when you don't want to see the computer drawing. For example the canvas could be on a page of a Notebook widget and you would simply display another empty page.

Instead of another new function I implemented the try except block inside the ThreadAutoRender class like so:

class QuitThread(Exception):
    pass
 
class ThreadAutoRender(Thread):
    def __init__(self):
        Thread.__init__(self)
        self.needs_to_render = False
        self.condition = Condition()
    def run(self):
        try:
            while True:
                self.wait_and_render()
        except QuitThread:
            pass
         
    def wait_and_render(self):
        with self.condition:
            if not program_is_running:
                raise QuitThread
            while not self.needs_to_render:
                self.condition.wait()
                if not program_is_running:
                    raise QuitThread
            self.needs_to_render = False
        try:
            render()
        except Exception as e:
            print('error: ', e)
 
thread_auto_render = ThreadAutoRender()
thread_auto_render.start()

[Gribouillis]

print('error: ', e)

This statement may display very little debugging information. Consider using traceback.print_exc() instead.

[philipbergwerf]

print('error: ', e)

This statement may display very little debugging information. Consider using traceback.print_exc() instead.

I don't understand... where is 'traceback' coming from? What is the correct way to print the default python error message e.g. Traceback (most recent call last):
blahblahblah?

[deanhystad]

traceback is a module in the standard Python library. "import traceback" creates a variable named "traceback" that references the module. traceback.print_exc() calls a function in the module.

https://docs.python.org/3/library/traceback.html

[philipbergwerf]

traceback is a module in the standard Python library. "import traceback" creates a variable named "traceback" that references the module. traceback.print_exc() calls a function in the module.

https://docs.python.org/3/library/traceback.html

Ah thank you for explaining. I want to thank everyone because I learned some neat tricks from this forum thread. I think the orginal question(how to handle a cpu intensive function) is answered fully now. You need to run it in a thread and there are some useful short code examples in this thread on how to call this thread function if you press a key.