Strange error with unbound method

[Remco Gerlich]

Fernando Rodríguez <spamers at must.die> wrote in comp.lang.python:
> 	I have a class called ParaStyle (see code below). This class has a
> method called makeBlackAndWhite that returns a new instance of class
> ParaStyle.
> 
> 	I want to transform a list of ParaStyle instances into a list of the
> result of applying the makeBlackAndWhite method of each instance.
> 
> 	If I do:
> paraStyles = map( ParaStyle.makeBlackAndWhite, paraStyles )
> 
> I get the following error:
> TypeError: unbound method must be called with class instance 1st argument
> 
> While if I do it with a for loop:
> l = []
> for para in paraStyles:
>     l.append( para.makeBlackAndWhite() )
> 
> I dont get any error!  =:-O
> 
> What's going on???? O:-)

In the first case you call a method on a class. That's not possible.

The second case, since the list contains *instances*, everything is ok. You
call the method on the instance.

You need a lambda to do it with map:
l = map(lambda style: style.makeBlackAndWhite(), paraStyles)

The lambda creates a temporary function that calls makeBlackAndWhite on the
argument it receives.

-- 
Remco Gerlich