DrConti wrote:
> I need a variable alias ( what in other languages you would call "a
> pointer" (c) or "a reference" (perl))
Or, you think you need it.
> I read some older mail articles and I found that the offcial position
> about that was that variable referencing wasn't implemented because
> it's considered bad style.
Generally, yes. The line goes, roughly, "You've decided on a solution
and are twisting your problem to fit it."
> There was also a suggestion to write a real problem where referencing
> is really needed. I have one...:
>
> I'm trying to generate dynamically class methods which works on
> predefined sets of object attributes.
> one of these is the set of attributes identfying uniquely the object
> (primary key).
First, this is _not_ a "real problem"; this is a bunch of code. The
"real problem" request is to provide an actual use case, not some code
where you want to write what you want to write.
> A naïve attempt to do the job:
>
> class ObjectClass:
> """ Test primary Key assignment """
>
> if __name__ == "__main__":
>
> ObjectClassInstantiated=ObjectClass()
> ObjectClassInstantiated.AnAttribute='First PK Elem'
> ObjectClassInstantiated.AnotherOne='Second PK Elem'
> ObjectClassInstantiated.Identifier=[]
>
> ObjectClassInstantiated.Identifier.append(ObjectClassInstantiated.AnAttribute)
>
> ObjectClassInstantiated.Identifier.append(ObjectClassInstantiated.AnotherOne)
> print ObjectClassInstantiated.Identifier
> ObjectClassInstantiated.AnAttribute='First PK Elem Changed'
> print ObjectClassInstantiated.Identifier
If you insist on this kind of approach, you could use a pair of
an object, and an attribute name as a "reference," and use getattr
and setattr to access the identified attribute. _But__ I emphasize
that you are thinking about your problem from the point of view
of a solution, not from the point of view of the problem.
You'd probably like this:
class Example(object):
""" Test primary Key assignment """
def __init__(self, one, two, other):
self.one = one
self.two = two
self.other = other
def __repr__(self):
return '%s(%r, %r, %r)' % (
type(self).__name__, self.one, self.two, self.other)
if __name__ == "__main__":
eg = Example(3.1415, 3+4j, 'pi')
ref_attr = eg, 'one'
ref_other = eg, 'other'
print eg, getattr(*ref_attr), getattr(*ref_other)
eg.one = 'First PK Elem'
print eg, getattr(*ref_attr), getattr(*ref_other)
setattr(*ref_other + (u'Strangely',))
print eg, getattr(*ref_attr), getattr(*ref_other)
But you might consider this:
class Another(Example):
""" Test primary Key assignment """
key = ('one', 'two')
def getkey(v):
return [getattr(v, part) for part in v.key]
if __name__ == "__main__":
eg2 = Another(3.1415, 3+4j, 'pi')
print eg2, getkey(eg2)
eg2.one = 'First PK Elem'
print eg2, getkey(eg2)
setattr(eg2, 'two', u'Strangely')
print eg2, getkey(eg2)
--
-Scott David Daniels
[EMAIL PROTECTED]
--
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