Passing additional arguments to event listeners ?

[Łukasz Czuja]

Hi,

I do not see anywhere in the docs a way to pass custom attributes to
event listeners:

event.listen(cls, 'before_insert', before_insert_listener, arg1, arg2,
kwarg1 = 'value', kwarg2 = 'value2')

so that the before_insert_listener can have mixed signature:

def before_insert_listener(mapper, connection, target, arg1, *args,
**kwargs):

the only other solution would be to store extra processing information
on the 'target' itself.

Should be reasonable if there is not another way to pass around
arguments. Should I open a ticket then?

Thanks

[Michael Bayer]

this kind of pollutes the API with kwargs that might be needed for the listen() function itself someday, these are external use cases that are easily handled in Python:

def before_insert_listener(arg1, arg2, k1='value', k2='value'):
def before_insert(mapper, conn, target):
... body
return before_insert

event.listen(cls, 'before_insert', before_insert_listener(arg1, arg2, k1='x', k2='y'))

[Tate Kim]

How about functools.partial ?
As far as I know, functools.partial will simply do this.

Usually, I import this when I need to make an argument-less function equip extra arguments.


Best regards,
Tate

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[Jackson, Cameron]

Not sure if this helps or not, but how about using a lambda that that calls your function with the arguments you want? This is the solution I've been using for passing arguments to wxPython event handlers. This tutorial might help: http://wiki.wxpython.org/Passing%20Arguments%20to%20Callbacks

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[Tate Kim]

Yes, I think also lambda can be good one.

Though lambda reduces an effort to type a predefined function, functools.partial is a bit familiar to me.

[Łukasz Czuja]

Thank you all for tips. I'll probably stick to the functools method
though.

I recommend adding a paragraph about this to docs as more people will
stumble upon this as this was possible with the extension system (one
could pass additional vars to extension constructor and use them in
callbacks) and no longer (directly) with events.

cheers.

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