Accessing class variable at class creation time

[Carlos]

Hi!

class A:
X = 2
def F():
print A.X
F()

The above fails because the name A is not
yet at global scope when the reference A.X
is reached. Is there any way to refer to A.X
without making explicit use of the name 'A'?
Admittedly the code looks pretty unusual,
but I'm defining configuration "minilangua ges"
to configure different parts of an application,
each inside a configuration class (like A),
and I find this very convenient except for
the above problem.

Thank you in advance
Regards,
Carlos

[Jan-Ole Esleben]

Re: Accessing class variable at class creation time

You could use self.__class__. X

HTH, Ole


23 Sep 2005 14:01:21 -0700, Carlos <carlosjosepita @gmail.com>:[color=blue]
> Hi!
>
> class A:
> X = 2
> def F():
> print A.X
> F()
>
> The above fails because the name A is not
> yet at global scope when the reference A.X
> is reached. Is there any way to refer to A.X
> without making explicit use of the name 'A'?
> Admittedly the code looks pretty unusual,
> but I'm defining configuration "minilangua ges"
> to configure different parts of an application,
> each inside a configuration class (like A),
> and I find this very convenient except for
> the above problem.
>
> Thank you in advance
> Regards,
> Carlos
>
> --
> http://mail.python.org/mailman/listinfo/python-list
>[/color]

[Simon Percivall]

Re: Accessing class variable at class creation time

It might be that I'm complicating something easy here, but I
immediately thought of

import sys

class A:
X = 2
def F():
f = sys._getframe() .f_back
print f.f_locals["X"]
F()

[Benji York]

Re: Accessing class variable at class creation time

Carlos wrote:[color=blue]
> Hi!
>
> class A:
> X = 2
> def F():
> print A.X
> F()
>
> The above fails because the name A is not
> yet at global scope when the reference A.X
> is reached. Is there any way to refer to A.X
> without making explicit use of the name 'A'?[/color]

How about this:
[color=blue][color=green][color=darkred]
>>> class A:[/color][/color][/color]
.... X = 2
.... print X
....
2
--
Benji York

[Jan-Ole Esleben]

Re: Accessing class variable at class creation time

That doesn't really give him a way of using the class variable inside a method.

Ole


2005/9/24, Benji York <benji@benjiyor k.com>:[color=blue]
> Carlos wrote:[color=green]
> > Hi!
> >
> > class A:
> > X = 2
> > def F():
> > print A.X
> > F()
> >
> > The above fails because the name A is not
> > yet at global scope when the reference A.X
> > is reached. Is there any way to refer to A.X
> > without making explicit use of the name 'A'?[/color]
>
> How about this:
>[color=green][color=darkred]
> >>> class A:[/color][/color]
> ... X = 2
> ... print X
> ...
> 2
> --
> Benji York
>
> --
> http://mail.python.org/mailman/listinfo/python-list
>[/color]

[Benji York]

Re: Accessing class variable at class creation time

Jan-Ole Esleben wrote:[color=blue]
> That doesn't really give him a way of using the class variable inside a method.[/color]

Oh! I must have misunderstood the question. I'd like to know more
about why the OP wants to do this; a small example would help narrow
down the possibilities.
--
Benji York

[Carlos]

Re: Accessing class variable at class creation time

Thank you all!

After all, I found at least three more or less convenient alternatives:

1) Pass X as default parameter to F.
2) Set globals() from inside A, something like globals()['A_locals'] =
locals() or globals()['A_X'] = X. Then access A_locals or A_X from F.
3) Use sys._getframe(1 ) or sys._getframe() .f_back to get the caller
frame.

But the following won't work:
[color=blue]
> self.__class__. X[/color]

Because there is no self around here, I'm not trying to access X from a
class instance but instead from code running at class definition time.
[color=blue]
> class A:
> ... X = 2
> ... print X[/color]

Of course this will print X but the point was to do it from inside a
function.

Regards,
Carlos

[Dave Hansen]

Re: Accessing class variable at class creation time

On 23 Sep 2005 14:01:21 -0700, "Carlos" <carlosjosepita @gmail.com>
wrote:
[color=blue]
>Hi!
>
>class A:
> X = 2
> def F():
> print A.X
> F()
>
>The above fails because the name A is not
>yet at global scope when the reference A.X[/color]

Maybe I'm missing something. Python 2.4.1#65 under Win32 Idle 1.1.1
gives me the following:

--begin included file---[color=blue][color=green][color=darkred]
>>> class A:[/color][/color][/color]
X = 2
def F():
print A.X
F()


2
---end included file---

But what good is F? You can't call A.F() because methods need an
instance, and calling A.F(instance) or instance.F() throws a TypeError
(argument count) exception.

Regards,

-=Dave
--
Change is inevitable, progress is not.