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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 visit_slice(self, node):
 """return an astroid.Slice node as string"""

        lower = node.lower.accept(self) if node.lower else ""
        upper = node.upper.accept(self) if node.upper else ""
        step = node.step.accept(self) if node.step else ""
        if step:
            return "%s:%s:%s" % (lower, upper, step)
        return "%s:%s" % (lower, upper)