+class VersioningBase(object):
+
+ def get_version(self, source_files):
+ raise NotImplementedError
+
+ def needs_update(self, output_file, source_files, version):
+ raise NotImplementedError
+
+class VersioningError(Exception):
+ """
+ This exception is raised when version creation fails
+ """
+ pass
\ No newline at end of file