handling many default values

[Gabriel Genellina]

At Friday 10/11/2006 14:11, Alan G Isaac wrote:

>My class MyClass reuses many default parameters
>with a small number of changes in each instance.
>For various reasons I decided to put all the
>parameters in a separate Params class, instances
>of which reset the default values based on keyword
>arguments, like this:
>
>class Params:
>      def __init__(self,**kwargs):
>          #set lots of default values
>          ...
>          #set the deviations from defaults
>          self.__dict__.update(kwargs)
>
>Is this a reasonable approach overall?
>(Including the last line.)

I'm not sure what you want to do exactly, but a class attribute acts 
as a default instance attribute.

class A(object):
     x = 0
     y = 20
     def __init__(self, x=None, y=None):
                 if x is not None: self.x = x
                 if y is not None: self.y = y

class B(A):
     z = 3
     def __init__(self, x=None, y=None, z=None):
                 A.__init__(self, x, y)
                 if z is not None: self.z = z

a = A(1)
print "a.x=",a.x
print "a.y=",a.y

b = B(z=8)
print "b.x=",b.x
print "b.y=",b.y
print "b.z=",b.z

output:

a.x= 1
a.y= 20
b.x= 0
b.y= 20
b.z= 8


-- 
Gabriel Genellina
Softlab SRL 

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