Fredrik Lundh wrote: > Kay Schluehr wrote: > > > I wonder why the isinstance() function is sensitive about the import > > path i.e. the result depends not only on the class and the instance but > > also on how a class is imported? > > isinstance uses class object identity. > > if you manage to import the same thing multiple times, you'll have > multiple class objects representing the same source code, and is- > instance won't work properly.
Importing a class/module multiple times does not cause the problem. Writing import ForeignPackage.B as B1 import ForeignPackage.B as B2 in C.py does not destroy the identity B1 == B2. Perhaps it is recovered from sys.modules["ForeignPackage.B"]? It is not actually isinstance() that depends on path information but the module recovery. The importer seems to disambiguate to greedy. > > > Example: > > > > MyPackage/ Top-level package > > __init__.py Initialize package > > __me__.py Module used for setting Python-path > > A.py Use objects of ForeignPackage and > > subpackages > > ForeignPackage/ Don't touch! > > __init__.py Initialize package > > B.py Defines class B1 > > MySubPackage/ Subpackage > > __init__.py Initialize subpackage > > C.py Defines instance checker for B1 instances > > in my newsreader, it looks like the C.py module is defined some- > where inbetween MyPackage and MyPackage/ForeignPackage. > what file system are you using? ;-) This is surprisingly irrelevant. I used __me__.py for several projects under Win2K without harm. Python seems to be more intelligent in path handling than Windows. > (I don't have the energy to decipher your convoluted import > and path-manipulation code; > but my intuition tells me that if > you flatten the hierarchy, put MyPackage and ForeignPackage > at the same level, and stop messing with the path inside the > __init__ files, your problems will just disappear). Flattening the package structure would solve the problem as well as destroying all file-system based packages and abandon them from Python. A bad joke? Yes, but managing all code using a database instaed of an OS dependent filesys would make sense to me. Ciao, Kay -- http://mail.python.org/mailman/listinfo/python-list
