Arthur Pemberton wrote:
> What is the best way to do data source abtraction? For example have
> different classes with the same interface, but different
> implementations.
>
> I was thinking of almost having classA as my main class, and have
> classA dynamically "absorb" classFood into to based on the extension
> of the input file received by classA. But this doesn't seem possible.
Could you explain more accurately what you're trying to do ? FWIW, it
seems that a plain old factory function would do ?
class DatasourceAbstraction(object):
""" base class, factoring common stuff """
# implementation here
class JpegFile(DatasourceAbstraction):
# ....
class PdfFile(DatasourceAbstraction):
# ....
class TxtFile(DatasourceAbstraction):
# ....
# etc
_classes = {
'jpg' : JpegFile,
'txt' : TxtFile,
'pdf' : PdfFile,
# etc..
}
def Datasource(inputfile):
ext = os.path.splitext(inputfile)
return _classes.get(ext, <SomeDefaultClassHere>)(inputfile)
The fact that there's no 'new' keyword in Python, and that classes are
callable objects acting as factories means that it's a no-brainer to use
a plain function (eventually disguised as a Class - the client code just
doesn't care !-) as factory...
Now if I missed the point, please give more explanations...
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bruno desthuilliers
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