[Python-ideas] operator.call / operator.__call__

[Antony Lee]

I have two use cases below.  Yes, it is true that just defining the "call"
function myself would only take me two lines, but on the other hand the
same is true for most functions in the operator module...

- Sometimes, depending on a switch, you want either to call a function
directly, or to pass it to a specialized "caller", e.g.

def run_in_thread(func, *args, **kwargs):
    Thread(target=func, args=args, kwargs=kwargs).start()

def run_here_or_in_thread(in_thread, func, *args, **kwargs):
    (run_in_thread if in_thread else operator.call)(func, *args, **kwargs)

or to optionally use a ContextDecorator:

def run_in_ctx(ctx, func, *args, **kwargs):
    (ctx or operator.call)(func)

- In Qt programs (although I assume similar ideas apply to other GUI
toolkits), where functions that operate on the GUI can only be called from
the main thread, but "signals" (in the Qt sense of the term) can be used to
communicate between threads, I find it useful to define a "call this in the
GUI thread" generic signal.  The implementation is essentially

class Main(QMainWindow):
    any_callable_signal = pyqtSignal(object)
    def __init__(self, *args, **kwargs):
        <...>
        self.any_callable_signal.connect(lambda f: f()) # <- operator.call
seems to express this better.
    def call_in_gui_thread(self, func):
        self.any_callable_signal.emit(func)

Antony

2014-10-29 17:57 GMT-07:00 Steven D'Aprano <steve at pearwood.info>:

> On Wed, Oct 29, 2014 at 03:39:59PM -0700, Antony Lee wrote:
> > A simple suggestion: add "operator.call" and "operator.__call__", which
> > would provide a function like Python2's "apply" (but it'd be called with
> > already unpacked arguments, i.e. operator.call(f, *args, **kwargs)).
> > Why?  To be able to pass it as an argument to other function, just like
> the
> > other functions defined in the "operator" module.
>
> I think you want something like this?
>
> def call(callable, *args, **kwargs):
>     return callable(*args, **kwargs)
>
>
> Can you give an example of how you might use this call method? It
> doesn't have to be a real world use-case, just an illustration.
>
> Perhaps I'm being a bit dim-witted today, but I'm having trouble
> thinking of where I would use this operator.call rather than just
> directly applying *args, **kwargs to the callable.
>
>
> --
> Steven
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