Huh? I guess you meant to reply to the OP, not me.
Cheers,
- Alf
* Javier Collado:
Hello,
I'd say that isn't totally incorrect to use strings instead of
symbols. Please note that in other programming languages symbols,
atoms and the like are in fact immutable strings, which is what python
provides by default.
Best regards,
Javier
2010/1/21 Alf P. Steinbach <al...@start.no>:
* Martin Drautzburg:
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?
def move( direction ):
... print( "move " + str( direction ) )
...
move( "up" )
move up
class using_directions:
... up = 42
... move( up )
...
move 42
up
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'up' is not defined
_
Of course it's an abuse of the language. :-)
So I wouldn't recommend it, but it's perhaps worth having seen it.
Cheers & hth.,
- Alf
PS: I hope this was not a homework question.
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