Fredrik Lundh wrote: > Kay Schluehr wrote: > > > > 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 > > that doesn't import it more than once; Python uses a cache to hold > modules, but the cache only works if Python can be sure that the > modules are the same thing, based on the information in the *import* > statement. in this case, "ForeignPackage.B" is clearly the same thing > as "ForeignPackage.B".
Yes, that's what I did expect. > if you change the path around (in your case, by adding MyPackage to > the path, rather than relying on path-relative import), you'll introduce > multiple ways to import the same module, and the cache won't work > properly. and when the cache doesn't work, isinstance breaks down > for the reason I stated. Exactly. "ForeignPackage.B" and "MyPackage.ForeignPackage.B" are two paths pointing to the same module but it will be imported twice because the cache does not lookup a strong name ( e.g. a hash of the module ) but the import path. This may also be the reason why it is not possible to import a module in an interactive session, than edit it and finally re-import it into the same running session. The hash value would have been changed but the path remains the same. > > > Flattening the package structure would solve the problem as well as > > destroying all file-system based packages and abandon them from Python. > > well, packages for just fine for me. In some cases they do, in other they don't. The __me__.py module comes from working with ClearCase where the Python package is not installed by an installation routine relative to an existing Python path. The package has to recognize it's own position somewhere relative to the virtual directory which can be arbitrary. Installing the package under site-packages/ is a no go. > if you cannot get them to work, > maybe you should stop doing things that don't work. For shure, but people tend to do workarounds. So I did. Regards, Kay -- http://mail.python.org/mailman/listinfo/python-list
