Symbols as parameters?

Martin Drautzburg Martin.Drautzburg at
Thu Jan 21 08:43:12 CET 2010

Hello all,

When passing parameters to a function, you sometimes need a paramter
which can only assume certain values, e.g.

        def move (direction):
If direction can only be "up", "down", "left" or "right", you can solve
this by passing strings, but this is not quite to the point:

        - you could pass invalid strings easily
        - you need to quote thigs, which is a nuisance
        - the parameter IS REALLY NOT A STRING, but a direction

Alternatively you could export such symbols, so when you "import *" you
have them available in the caller's namespace. But that forces you
to "import *" which pollutes your namespace.

What I am really looking for is a way

        - to be able to call move(up)
        - having the "up" symbol only in the context of the function call

So it should look something like this

... magic, magic ...
... unmagic, unmagic ...
print up

This should complain that "up" is not defined during the "print" call,
but not when move() is called. And of course there should be as little
magic as possible.

Any way to achieve this?

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