def get_package_dir(self, package):
        """Return the directory, relative to the top of the source
        distribution, where package 'package' should be found
        (at least according to the 'package_dir' option, if any)."""
        path = package.split('.')

        if not self.package_dir:
            if path:
                return os.path.join(*path)
            else:
                return ''
        else:
            tail = []
            while path:
                try:
                    pdir = self.package_dir['.'.join(path)]
                except KeyError:
                    tail.insert(0, path[-1])
                    del path[-1]
                else:
                    tail.insert(0, pdir)
                    return os.path.join(*tail)
            else:
                # Oops, got all the way through 'path' without finding a
                # match in package_dir.  If package_dir defines a directory
                # for the root (nameless) package, then fallback on it;
                # otherwise, we might as well have not consulted
                # package_dir at all, as we just use the directory implied
                # by 'tail' (which should be the same as the original value
                # of 'path' at this point).
                pdir = self.package_dir.get('')
                if pdir is not None:
                    tail.insert(0, pdir)

                if tail:
                    return os.path.join(*tail)
                else:
                    return ''
Return the directory, relative to the top of the source
        distribution, where package 'package' should be found
        (at least according to the 'package_dir' option, if any).
product/gradle-plugin/src/main/python/setuptools/_distutils/command/build_py.py