Question related to the thread Multithreading PyQt applications with QThreadPool

by Martin Fitzpatrick Last updated PyQt5 FAQ
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bharathinmail5419 | 2020-07-19 10:31:58 UTC | #1

Can you explain more how

python 
    # Add the callback to our kwargs
    self.kwargs['**progress_callback**'] = self.signals.progress

had binded to the below function

python 
    def execute_this_fn(self, progress_callback):
        for n in range(0, 5):
            time.sleep(1)
            progress_callback.emit(n*100/4)

martin | 2020-07-19 10:39:49 UTC | #2

Hey @bharathinmail5419 welcomet to the forum!

This is making use of Python keyword unpacking. This allows you to pass keyword parameters to functions using a dictionary of key=value pairs.

When we call the execute_this_fn we call it with the following ...

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python 
execute_this_fn(**self.kwargs)

This unpacks the key=value pairs in the self.kwargs dictionary, as keywords for the function. So for example, if we had the following dictionary

python 
my_dict = {
'something': 3,
'another': 6,
}

and then called a function as follows...

python 
my_function(**my_dict)

this would be the equivalent of ...

python 
my_function(something=3, another=6)

So, going back to the original example. We have a dictionary called kwargs which holds keyword arguments. We add another entry to that dictionary called 'progress_callback' which holds the function we're going to call. That could be anything, but for example say we stored the print function --

python 
kwargs = {}
kwargs['progress_callback'] = print   # Store the print function in this dictionary

If we then called our function with...

python 
execute_this_fn(**kwargs)

That would be the equivalent of calling

python 
execute_this_fn(progress_callback=print)

The value stored in the dictionary under progress_callback is passed as an argument with that keyword to the function.

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Question related to the thread Multithreading PyQt applications with QThreadPool was written by Martin Fitzpatrick .

Martin Fitzpatrick has been developing Python/Qt apps for 8 years. Building desktop applications to make data-analysis tools more user-friendly, Python was the obvious choice. Starting with Tk, later moving to wxWidgets and finally adopting PyQt.

Question related to the thread Multithreading PyQt applications with QThreadPool was published in faq on (updated ) . Feedback & Corrections welcome in our public issue tracker.

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