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How can I force the use-only-after-declaration?

Lexy Zhitenev zhitenev at cs.vsu.ru
Thu Dec 19 07:48:24 EST 2002 
> Hi!
>
> In other languages, I am used to declare variables before the use.
> The translators for those languages give me an error/warning if I use a
> variable that has not been declared.
>
> Example (C-like syntax):
>
>     ...
>
>     int a, c;
>
>     a = 100; /* Ok! */
>     b = 200; /* Error! */
>     c = 300; /* Ok! */
>
>     ...
>
> There is a way to emulate it using Python?
>

In Python 2.2 you can define some slots in a class and access them. When you
try to access an undefined slot, you get an AttributeError. This is is a bit
tricky and classes are somewhat slower than ordinary variables. But if you
need it, look here.

>>> class somestruct(object):
...               def __init__(self):
...                       self.__slots__ = ['a','c']
>>> r = somestruct()
>>> r.a = 1
>>> r.c = 'Hi!'
>>> r.b = ['a']
Traceback bla-bla-bla AttributeError.

I could have missed some syntax formalities (I don't have Python here), but
the idea is this like.

Regards, Lexy.
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