Is it possible to call a callback function which may declare no arguments but then pass some arguments at call time without raising exception?

Question

Is it possible to have the below code without raising an exception?
The hello function represents code outside my control. It is only here for the sake of clarity.

def hello():
    print("hellowed")

def callsCallback(callback):
    callback(*["dd"])

callsCallback(hello)

The idea is for a library to receive a callback function for when something happens. For backwards compatibility, the function being called may or may not receive parameters.

I'm aware of this answer: How can I find the number of arguments of a Python function? but I'd rather avoid inspection, if I can.

You can't avoid inspection then. Python isn't javascript, it's not going to ignore arguments a function doesn't expect. — SilverSlash, Jan 27 '18 at 10:32
You could make a wrapper function stripping unwanted arguments. — VPfB, Jan 27 '18 at 10:32
@SilverSlash I'm just trying to make sure I did my research right. — brunoais, Jan 27 '18 at 10:33
@VPfB How do I know which arguments are not wanted, then? Only inspection, right? — brunoais, Jan 27 '18 at 10:34
@brunoais The title says no arguments. But in general either you know or you do the inspection. — VPfB, Jan 27 '18 at 10:46

kdheepak · Answer 1 · 2018-01-29T14:06:07.503

0

If you used *args in a wrapper function then it would never throw an exception because of the incorrect number of arguments.

def hello():
    print("hellowed")

def wrapper(f):
    def g(*args):
        f() 
    return g

def callsCallback(callback):
    callback = wrapper(callback)
    callback(*["dd"])

callsCallback(hello)

You could use a decorator style function. This may be overkill for what you want to do.

If you don't know ahead of time how many arguments hello takes, you would have to introspect as you suggested to call the function appropriately.

edited Jan 29 '18 at 14:06

answered Jan 27 '18 at 10:28

kdheepak

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`def hello()` is from outside my code. I added redundancy to that fact to make the question more clear. – brunoais Jan 27 '18 at 10:30
Thanks for the clarification. I've updated the answer above to make it more closer to what you want. – kdheepak Jan 27 '18 at 23:30
You sure it is correct? The wrapper function doesn't do anything. – brunoais Jan 28 '18 at 10:04
Sorry, meant to say `return g`. I've edited the above answer. – kdheepak Jan 29 '18 at 14:06
Still doesn't do what I need but it does something useful. – brunoais Jan 29 '18 at 19:22

Is it possible to call a callback function which may declare no arguments but then pass some arguments at call time without raising exception?

1 Answers1