QtConcurrent in PySide/PyQt

Question

I'm trying to figure out if subclassing QtConcurrent and writing a run method inside it will work:

class Task(QtCore.QtConcurrent):

     def run(self, function):
           function()

Or is it completely useless?

Why won't you give it a try? – pacholik Sep 03 '15 at 14:55 — pacholik, Sep 03 '15 at 14:55

score 18 · Accepted Answer · answered Sep 03 '15 at 15:52

18

It's completely useless, because QtConcurrent is a namespace, not a class.

Also, neither PyQt nor PySide provide any of the functionality provided by QtConcurrent, because it's all template-based and therefore impossible to wrap.

PS: the PySide documentation you linked to is for the ReduceOption enum. Since it's doubtful whether that enum has any use outside the QtConcurrent namespace, it's probably a bug that PySide includes it.

answered Sep 03 '15 at 15:52

ekhumoro

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Very interesting. I was just about to experiment a little bit with `QtConcurrent` in PyQt5 when I realized that I can't find anything. Thanks for the hint. I guess C++ it is. :D – rbaleksandar Sep 05 '16 at 15:08
Might it be possible for someone to rewrite all this QtConcurrent in Python? I assume it wouldn't be very easy, but might it be possible? It seems frustrating that we have Futures in Python's concurrent.futures but PyQt5 is stuck in the Dark Ages. – mike rodent Jan 04 '22 at 14:26
@mikerodent [Templates](https://en.wikipedia.org/wiki/Template_(C%2B%2B)) are a C++ feature, which means `QtConcurrent` cannot be implemented in any meaningful sense in Python. You might be able to come up with some alternative API that reproduced *some* of the functionality, but it wouldn't really be `QtConcurrent` any more (e.g. [qconcurrent.py](https://gist.github.com/ales-erjavec/5ef43c5b3907a9e4924eec09bfb9d9c6)). I doubt whether it would ever be worth anyone's time trying to reproduce *all of it*, though (certainly the author of PyQt has never shown any interest in doing so when asked). – ekhumoro Jan 04 '22 at 18:25

score 0 · Answer 2 · answered Apr 24 '18 at 07:26

0

The class you are looking for is QRunnable.

answered Apr 24 '18 at 07:26

Grumbel

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That does not provide the ability to call any function I don't think... Only option here is to inherit from QThread. See my solution above. – MathCrackExchange Mar 04 '19 at 22:25

score 0 · Answer 3 · answered Mar 04 '19 at 22:23

I am stuck on the same problem in PyQt5. I guess the only solution is to do this locally:

def connect(self):
    class ConnectThread(QThread):
        def __init__(self, func):
            super().__init__()
            self.func = func
        def run(self):
            self.func()
    self.connectThread = ConnectThread(self._connect)
    self.connectThread.start()

def _connect(self):
    if self._driver is None:
        uri = self.uriString()
        if uri and self.user and self.password:
            self.statusMessage.emit("Connecting to the Graph Database....", -1, "color:blue;")
            try:
                self._driver = GraphDatabase.driver(uri, auth=(self.user, self.password))
                self.statusMessage.emit("Connected!", 5000, "color:green;")
            except Exception as e:
                self.clearStatusMessage.emit()
                Error(str(e)).exec_()
                if __debug__:
                    raise e

And remember to set the thread to a member variable: self.thread = ... or else your thread reference will go out of scope, and most likely the thread object deleted.

You could also move your function-to-call into a local definition of it as Python allows both nested functions and classes within one another!

QtConcurrent in PySide/PyQt

3 Answers3