Expression problem.

[Nethirlon .]

On 6 okt, 15:25, Peter Otten <__pete... at web.de> wrote:
> Nethirlon . wrote:
> > On 6 okt, 11:53, Peter Otten <__pete... at 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 "<stdin>", 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!