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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 get_value(self, context):
 """Run python eval on the input string."""

        if self.value:
            return expressions.eval_string(self.value, context)
        else:
            # Empty input raises cryptic EOF syntax err, this more human
            # friendly
            raise ValueError('!py string expression is empty. It must be a '
                             'valid python expression instead.')