Mailing List Archive

A while back I asked how to pass parameterized callbacks to Tkinter.
Now I need to explore how best to do partial resolution of callback
arguments. For example, define values for arguments 1 and 2 at
registration time, but leave argument 3 to be populated by Tkinter.

Probably makes no sense. So let me use an example:

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For simple callbacks you can use a lambda or function wrapper:

def SetColor( color ):
print color

wgt1.configure( command = lambda color="red" : SetColor(color) )
wgt1.configure( command = lambda color="blue": SetColor(color) )

One suggestion Thomas Heller offered before was to use a callable object
instead; this gives a much simpler appearance:

def SetColor( color ):
print color

wgt1.configure( command = Call( SetColor, "red" ) )
wgt1.configure( command = Call( SetColor, "blue" ) )

(Call class source attached below in case you're interested).

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The wrinkle now is what if SetColor is an event callback (i.e. Tkinter
provides an event argument):

def SetColor( color, event ):
print color

this breaks the callable object form:
wgt1.configure( command = Call( SetColor, "red" ) )

with Tkinter giving:
TypeError: too many arguments; expected 1, got 2

So my quetsion is, can the "callable object" be used? Or do I have to fall
back to a lambda wrapper?

Thanks,

Randall



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class Call:
"""Instances of this class store a function as well as a list of arguments.
When they are called, the function will be called together with the
arguments used for creating the instance.
Slightly different than lambda, but nicer syntax."""

def __init__ (self, func, *args):
self.func = func # save the function (or bound method,or ...)
self.args = args # save the arguments to use
def __call__ (self):
apply (self.func, self.args) # call function, using args as arguments.
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