Symbols as parameters?

Jean-Michel Pichavant jeanmichel at sequans.com
Thu Jan 21 11:57:18 CET 2010


Martin Drautzburg wrote:
> 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 ...
> move(up)
> ... 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?
>
>   
in move.py

def move(direction):
    print "moving %s" % direction

move.UP = 'up'
move.DOWN = 'down'

Then

 >>> from move import move
 >>> move(move.UP)
moving up


JM



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