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structseq and keywords?

Michael Hudson mwh at python.net
Wed Mar 13 05:20:57 EST 2002 
quinn at vomit.ugcs.caltech.edu (Quinn Dunkan) writes:

> Is structseq supposed to take keyword args?  From the source I assume it was
> meant to, but they're unused.

Well, in 2.2 it takes one keyword argument -- "sequence".  In 2.2.1
and 2.3 it will take another one -- "dict".  This is the result of
some hacking I did a week or so ago related to pickling the buggers.

> I suppose they'd interact poorly with sequence args, but I'd expect
> them to be mutually exclusive:
> 
> ss(attr=bar) #-> attr set to bar, rest set to None
> ss(a, b, c) #-> initialize with (a, b, c)

You'd have to write that last

ss((a,b,c))

...

> It also seems odd that structseq expects a single sequence rather than a
> variable number of args.

... but it seems you already know this.

In the current implementation, you're not really expected to create
structseq objects.  Why would you?

> I've been meaning to give python access to structseqs, since I think
> it would be useful for python as well as C code.

Hmm.  I think they're a bit specialized for that.  You could probably
whip up something nearly equivalent...

class StructSeq(object):
    def __init__(self, *args, **kw):
        slots = self.__class__.__slots__[:]
        for name, arg in zip(slots, args):
            setattr(self, name, arg)
            slots.remove(name)
        for key in kw:
            if key not in slots:
                raise ValueError
            setattr(self, key, kw[key])
            slots.remove(key)
        for name in slots:
            setattr(self, name, None)
    def __getitem__(self, i):
        return getattr(self, self.__class__.__slots__[i])

class stat_result(StructSeq):
    __slots__ = ['st_size', 'st_dev', 'st_atime']

>>> sr = stat_result(2, st_atime=3)
>>> sr.st_size
2
>>> sr[1]
>>> sr = stat_result(2, st_size=3)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "<stdin>", line 9, in __init__
ValueError
>>> tuple(sr)
(2, None, 3)
>>>

Doesn't do everything structseqs do, but that's mostly a matter of
typing.

Cheers,
M.

-- 
  Windows installation day one.  Getting rid of the old windows 
  was easy - they fell apart quite happily, and certainly wont 
  be re-installable anywhere else.   -- http://www.linux.org.uk/diary/
                                       (not *that* sort of windows...)
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