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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 walk_tree(self, top=None):
 """ Navigate all the groups in the file starting from top. If top is None, the root group is used. """

        if top is None:
            top = self.rootgrp

        values = top.groups.values()
        yield values
        for value in top.groups.values():
            for children in self.walk_tree(value):
                yield children