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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _target_classes(self, target):
 """Set of target's provided classes. Call at the target level is to memoize efficiently. """

    target_classes = set()
    contents = ClasspathUtil.classpath_contents((target,), self.runtime_classpath)
    for f in contents:
      classname = ClasspathUtil.classname_for_rel_classfile(f)
      if classname:
        target_classes.add(classname)
    return target_classes