> 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.
<snip/>
Use a factory function:
class UriBase(object):
REGISTRY = {}
class HttpUri(UriBase):
pass
UriBase.REGISTRY['http'] = HttpUri
def URI(arg):
return UriBase.REGISTRY[get_protocol(arg)](arg)
This is untested and could be enhanced by e.g. using metaclasses to perform
the registration automagicall, but I think you get the idea.
Diez
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