def evaluate(self, item):
if self.expr2 is None:<EOL><INDENT>return self.expr1.evaluate(item)<EOL><DEDENT>v1, v2 = self.expr1.evaluate(item), self.expr2.evaluate(item)<EOL>try:<EOL><INDENT>return OP_MAP[self.op](v1, v2)<EOL><DEDENT>except TypeError as e:<EOL><INDENT>return e<EOL><DEDENT>
Evaluate this expression for a partiular item