On Jan 23, 5:09 am, GiBo <[EMAIL PROTECTED]> wrote:
> Hi all,
>
> I have a class URI and a bunch of derived sub-classes for example
> HttpURI, FtpURI, HttpsURI, etc. (this is an example, I know there is
> module urllib & friends, however my actual problem however maps very
> well to this example).
>
> Now I want to pass a string to constructor of URI() and get an instance
> of one of the subclasses back. For example uri=URI('http://abcd/...')
> will make 'uri' an instance of HttpURI class, not instance of URI.
>
> To achieve this I have a list of all subclasses of URI and try to
> instantiate one by one in URI.__new__(). In the case I pass e.g. FTP URI
> to HttpURI constructor it raises ValueError exception and I want to test
> HttpsURI, FtpURI, etc.
>
> For now I have this code:
>
> =====
> class URI(object):
> def __new__(self, arg):
> for subclass in subclasses:
> try:
> instance = object.__new__(subclass, arg)
> return instance
> except ValueError, e:
> print "Ignoring: %s" % e
> raise ValueError("URI format not recognized" % arg)
>
<snip>
Call __new__ and subclass.__init__ explicitly:
class URI(object):
def __new__(self, arg):
for subclass in subclasses:
try:
instance = object.__new__(subclass)
instance.__init__(arg)
return instance
except ValueError, e:
print "Ignoring: %s" % e
raise ValueError("URI format not recognized" % arg)
(Might I suggest 4-space indents vs. 8?)
-- Paul
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