Expression problem.

[Nethirlon .]

Hi,

I am having trouble with an expression.

I have the following line of code:

self.failUnless(c.as == 65215)

What happens when you compile this is that you get a syntax error.
This is because as has been made a keyword. failUnless is from the
module unittest.

Now my problem is this. the ".as" is no where defined in the code. The
code builds just fine if you removed it. But the origigal programmer
must have put it in for a reason. I just cant understand what that is.

Can anyone point me into the right direction? was ".as" before it
became a keyword some kind of string manipulator?

Let me know if you need more info.
Thanks
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Re: Expression problem.

[Nethirlon .]

On 6 okt, 11:53, Peter Otten <__pete...@web.de> wrote:
> Sebastiaan de Haan wrote:
> > Thank you Chris,
>
> > I'll try and find the attribute in the code. That was my conclusion
> > aswell... The original author must have defined it somewhere...
>
> Don't forget to check whether the object's class (or any of its bases) has a
> __getattr__() or __getattribute__() method.
>
> >>> class A(object):
>
> ...     def __getattr__(self, name):
> ...             return 42
> ...>>> a = A()
> >>> a.as
>
>   File "", line 1
>     a.as
>        ^
> SyntaxError: invalid syntax
>
> Note tha you can still access such an attribute using getattr()
>
> >>> getattr(a, "as")
>
> 42
>
> Peter

Thank you Peter,

While searching the document I found the following code:

class Open(dpkt.Packet):
__hdr__ = (
('v', 'B', 4),
('as', 'H', 0),
('holdtime', 'H', 0),
('identifier', 'I', 0),
('param_len', 'B', 0)
)

So, I am new at programming with Python, but doing my best to grasp
the concept here. From what I am understanding is that the __hdr__ is
something that the original programmer cameup with for him self. I am
just curious as to weather the "as" in this piece of code is the one I
am searching for.

Thanks in advance.
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Re: Expression problem.

[Nethirlon .]

On 6 okt, 15:25, Peter Otten <__pete...@web.de> wrote:
> Nethirlon . wrote:
> > On 6 okt, 11:53, Peter Otten <__pete...@web.de> wrote:
> >> Sebastiaan de Haan wrote:
> >> > Thank you Chris,
>
> >> > I'll try and find the attribute in the code. That was my conclusion
> >> > aswell... The original author must have defined it somewhere...
>
> >> Don't forget to check whether the object's class (or any of its bases)
> >> has a __getattr__() or __getattribute__() method.
>
> >> >>> class A(object):
>
> >> ...     def __getattr__(self, name):
> >> ...             return 42
> >> ...>>> a = A()
> >> >>> a.as
>
> >> File "", line 1
> >> a.as
> >> ^
> >> SyntaxError: invalid syntax
>
> >> Note tha you can still access such an attribute using getattr()
>
> >> >>> getattr(a, "as")
>
> >> 42
>
> >> Peter
>
> > Thank you Peter,
>
> > While searching the document I found the following code:
>
> > class Open(dpkt.Packet):
> >         __hdr__ = (
> >             ('v', 'B', 4),
> >             ('as', 'H', 0),
> >             ('holdtime', 'H', 0),
> >             ('identifier', 'I', 0),
> >             ('param_len', 'B', 0)
> >             )
>
> > So, I am new at programming with Python, but doing my best to grasp
> > the concept here. From what I am understanding is that the __hdr__ is
> > something that the original programmer cameup with for him self. I am
> > just curious as to weather the "as" in this piece of code is the one I
> > am searching for.
>
> Side note: if the code you have questions about is publicly available it's
> always a good idea to give the url. I am assuming that you are referring to
> an older version to this beast:
>
> http://code.google.com/p/dpkt/source/browse/trunk/dpkt/bgp.py
>
> Here's where your problem was fixed/adjusted to newer Python 
> versions:http://code.google.com/p/dpkt/source/detail?r=51
>
> The __hdr__ is indeed an invention of the author of the package, and is feed
> to the metaclass* of dpkt.Packet. The metaclass uses it to create __slots__
> that are filled dynamically in Packet.__init__().
>
> I recommend that you read the docstring of the Packet class
>
> http://code.google.com/p/dpkt/source/browse/trunk/dpkt/dpkt.py
>
> but only bother about the implementation if you cannot avoid it.
> You can always have a second look after you have gained some Python
> experience.
>
> Peter
>
> (*) Every class in Python is an instance of its metaclass, i. e. the
> relation between metaclass and class is the same as between class and
> instance. Custom metaclasses are a powerful feature, but tend to make Python
> code harder to grasp.

Peter,

Thank you very much, I did not know that the code was available
online, and also did not know that the author updated it online.

The package I was using came from the openSuse python repository,
given to me by one of the maintainers of that repository.

I am having a hard time understanding the concept of classes, so I
think that I should focus on that first, before continueing to try and
contribute.

Thank you very much for your help!

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