Newbie Alert: Help me store constants pythonically

[Francesco Bochicchio]

Il Sun, 06 Nov 2005 08:33:17 -0800, Brendan ha scritto:

> Hi all
> 
> I'm new to Python (and programming in general), and I can't decide what
> is the most 'pythonic' way to approach a problem.  Your advice would be
> appreciated.
> 
> I have a bunch of 'scans', containing the data measured from one of
> several types of 'model'. Each 'model' has different values for a list
> of constants  I want to create 'analyses' which interpret the data from
> the scans, with reference the appropriate model.  So far, I have come
> up with three strategies to store this information, illustrated below
> (I've simplified the constant list to just two):
> 
> 1) Store the model constants as class instances:
> 
> class Model:
>     def __init__(self, numBumps, sizeOfBumps):
>         self.__dict__.update(locals()); del self.self
> 
> MODEL1 = Model(1, 2)
> MODEL2 = Model(3, 4)
> #etc
> 
> class Analysis:
>     def __init__(self, scanData, model):
>         #do analysis
> 
> 2) Store the model constants as class variables:
> 
> class MODEL1:
>     numBumps = 1
>     sizeOfBumps = 2
> 
> class MODEL2:
>     numBumps = 3
>     sizeOfBumps = 4
> 
> class Analysis:
>     #as with 1
> 
> 3) Store the model constants as class variables of the analysis class:
> 
> class Model1Analysis:
>     numBumps = 1
>     sizeOfBumps = 2
> 
>     def __init__(self, scanData):
>        #do analysis
> 
> class Model2Analysis(Model1Analysis):
>     numBumps = 3
>     sizeOfBumps = 4
> 
> There may be more options, but at this point I became paralyzed with
> choice.  I worry about getting stuck with an unworkable structure since
> I don't have the experience to decide the merits of each in advance.  I
> get way too frustrated about these things :)
>    Brendan


My vote would go to the first option, but I don't understand why you use
such a complicate way to set instance attributes. I would do simply

  class Model:
     def __init__(self, numBumps, sizeOfBumps):
         self.numBumps = numBumps
	 self.sizeofBumps = sizeOfBumps

or, if you want to generalize the arguments of the constructor:

  class Model:
	def __init__(self, **model_attributes):
		for attname, attvalue in model_attributes.items():
			setattr(self, attname, attvalue)

As for why to choose the first option... is the one that causes you to
avoid useless code repetitions and to keep the Analysis code nicely
generic. 

Ciao
-----
FB