define

[Alex Martelli]

<posted & mailed>

Turhan Ozen wrote:

> I have a long list of parameters. I want to keep them in an array in
> order to pass them to functions. But I want to use the name of each
> parameter in the formulas to make them easy to read. I can use x[index]
> in the formulas. I am trying to have another name for each  x[index]. If
> I do anything to this secondary reference, the same is done to the
> corresponding x[index].
> 
> It is possible to do this in C and it looks more readable.

It looks to me that a good solution is a "list with named items" class.
E.g., in Python 2.3 (warning, untested code):

class list_with_names(list):
    def __init__(self, names):
        list.__init__(self, len(names)*[None])
        self.__names = {}
        for i, name in enumerate(names):
            self.__names[name] = i
    def __getattr__(self, name):
        try: return self.__names[name]
        except KeyError: raise AttributeError
    def __setattr__(self, name, value):
        try: self[self.__names[name]] = value
        except LookupError: object.__setattr__(self, name, value)

So instead of keeping your values in an 'array' (?), you'll do:

# e.g. a list of 5 items
x = list_with_names('aname another yetanother onemore andthistoo')

and then you can access and/or set e.g. x[1] equivalently to
x.another.  Why you would want to use indexed access as well as
named access, I don't know, but surely it's MUCH clearer and more
readable if any access on an item of x does use x.something rather
than just a bare unqualified 'something' as the name!


Alex