Question

Why I can’t redefine the __and__ operator?

class Cut(object):
      def __init__(self, cut):
         self.cut = cut
      def __and__(self, other):
         return Cut("(" + self.cut + ") && (" + other.cut + ")")

a = Cut("a>0") 
b = Cut("b>0")
c = a and b
print c.cut()

I want (a>0) && (b>0), but I got b, that the usual behaviour of and

Answer 1

__and__ is the binary (bitwise) & operator, not the logical and operator.

Because the and operator is a short-circuit operator, it can’t be implemented as a function. That is, if the first argument is false, the second argument isn’t evaluated at all. If you try to implement that as a function, both arguments have to be evaluated before the function can be invoked.