Aproblem with the short-circuit evaluation of logical operators is that they are not commutative, because they might raise exceptions: e. g., if x is 0, Python evaluates x!=0 and 1/x<2 to False, but evaluates 1/x<2 and x!=0 by raising an exception: it attempts to divide by 0 in the left conjunct. Define the XBool class so that each XBool object is a special representation of either the bool True, the bool False, or an exception being raised when trying to compute its bool value. Write a commutative and operator for XBools: writing XBool('x!=0') and XBool('1/x<2') evaluates to the XBool representing False; so does writing XBool('1/x<2') and XBool('x!=0').

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