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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 evaluate(self, env):
 """Evaluate the symbol in the environment, returning a Unicode string. """

        if self.ident in env.values:
            # Substitute for a value.
            return env.values[self.ident]
        else:
            # Keep original text.
            return self.original