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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 expression(self, previous_precedence=0):
 """An expression is an atom or an infix expression. Grammar (sort of, actually a precedence-climbing parser):
 expression = atom [ binary_operator expression ] . Args: previous_precedence: What operator precedence should we start with? """

        lhs = self.atom()

        return self.operator(lhs, previous_precedence)