adding parameter to python callback [duplicate]

Question

I am a beginner in Python, and I would like to add a parameter to a callback, in addition to the self and the event. I have tried with lambda, but without success.
My code at the moment looks like this :

control = monitor(block, callback=self.model)

And my model is :

def model(self, transaction)

I would like to have :

def model(self, file, transaction)

file being a string parameter I would like to pass to my "model" I tried by changing the control line in :

control = monitor(block, lambda transaction, args=args:    callback=self.model(transaction, args)

but this does not work, and it is getting too advanced but my python knowledge.
I get the following Error : "SyntaxError: lambda cannot contain assignment", I guess because of the = symbol.

Could you help me by explaining how I should proceed/what I am doing wrong ?

Gribouillis · Accepted Answer · 2016-12-10 18:29:47Z

10

Many times, when you think about using lambda, it is best to use functools.partial() which performs currying (or curryfication). You can use

from functools import partial

def model(self, transaction, file=None):
    ...

control = monitor(block, callback=partial(self.model, file='foobar'))

To answer your comment below, if you really need a true function, you can design you own:

def callback(func, **kwargs):
    @functools.wraps(func)
    def wrapper(*a, **k):
        return functools.partial(func, **kwargs)(*a, **k)
    return wrapper

control = monitor(block, callback=callback(self.model, file='foobar'))

edited Dec 10, 2016 at 18:29

answered Dec 10, 2016 at 17:31

Gribouillis

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1 Comment

user1654361 Over a year ago

Thanks, this works, and answers the question. I just get a side issue since partial have no name attribute whereas callback does. I check for this parameter somewhere else in some external code that I will change accordingly...

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