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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 changed(self, node=None, allowcache=False):
 """ Returns if the node is up-to-date with respect to the BuildInfo stored last time it was built. For File nodes this is basically a wrapper around Node.changed(), but we allow the return value to get cached after the reference to the Executor got released in release_target_info(). @see: Node.changed() """

        if node is None:
            try:
                return self._memo['changed']
            except KeyError:
                pass

        has_changed = SCons.Node.Node.changed(self, node)
        if allowcache:
            self._memo['changed'] = has_changed
        return has_changed