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Hi forum,

searching through the internet gave me the impression that I lack the right search terms for my problem. I may not even know enough python to ask the right question. But I trust in you.

I would like to have a python program do its webserver background chores with flask and a second thread that checks the serial input for data. When that serial data happens to add up to a meaningful message, it shall be transferred to the main thread and update the web site.

I have not yet seen events, subscriptions or event handlers as I know them from C#. I would have gone single-threaded if I had. But I seem to have to use a blocking Serial.Read() and let it hang in a separate thread.

Then I would like to create an event have an event handler that runs in the main thread (InvokeRequired(), anyone?). But python doesn't seem to work that way.

So my basic question: Does python even run an event loop that the humble programmer can use and I am too blind to find it?

Or would it be OK to just run my event handler from the serial-input-watching thread and there is no pitfall to this?

What I have tried:

def __init__(self, commPort:Serial):
    self._commPort = commPort
    self._inputMessageQueue = list()
    self._commThread = threading.Thread(daemon=True, target=self._ObserveComm, args=(self,))

def _ObserveComm(self):
        oneByte = bytearray(
        if(len(oneByte) > 0):
            oneMessage = Message.Parse(oneByte)
            if(issubclass(type(oneMessage), Message)):
Updated 16-Feb-21 4:04am

lukeer 9-Feb-21 14:30pm
Yes, there are events in threading.
But as far as I understand it, I would still have to create an endless loop in the main thread that polls the event.
Did I miss the part where I can attach a function to the event? Or does python work differently?
Richard MacCutchan 11-Feb-21 9:30am
I do not think Python has such a mechanism natively, but there may be a library that does it.
Richard MacCutchan 11-Feb-21 9:33am
Does python even run an event loop that the humble programmer can use and I am too blind to find it?

No, unless you add such a loop by yourself or use a library/framework that sets up an event loop for you. By itself, Python is a traditional sequential language that executes a program from beginning to end.
Richard MacCutchan 11-Feb-21 9:25am
It does have an event mechanism, see the link in my post above.
markkuk 11-Feb-21 10:21am
That's an add-on package, not part of the language specification. It's an example of "a library/framework that sets up an event loop" as I mentioned in my post. There are others, like most GUI frameworks.
Richard MacCutchan 11-Feb-21 10:41am
Quote: Changed in version 3.7: This module used to be optional, it is now always available.
Finally opted for blinker[^] for an event system since flask used it anyway.

Thank you all.

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