我可以在Python中定义一个“非”运​​算符吗？

Question

I am trying to interface a C++ library that implements logical operators &&, ||, ! (unary operator not) to operate on custom selection classes.

I'm a bit stuck because I can't find an unary 'not' operator in Python. Is it possible to override the built in ' not ' operator which works on boolean in Python ?

Is there another suitable operator, or do I need to define a function 'Not()' to implement this behavior?

Answer 1

You cannot override the boolean operators ( and , or , and not ) with special method hooks, because and and or operate lazily and a special method would require that you evaluate operands early instead.

You can only influence how the object is evaluated to a boolean (using the __nonzero__ or __len__ methods, depending on whether you are implementing a numeric or container type; Python 3 renamed __nonzero__ to __bool__ ).

You can hook into bitwise operators ( & , | and ~ ), with the __and__ , __or__ , and __invert__ methods, however. This is probably what you are looking for instead. For & and | there are also inverse and in-place hooks available ( __rand__ , __ror__ , __iand__ and __ior__ ).

The result of the boolean hooks ( __nonzero__ , etc.) are cast to a boolean ( True or False ), but the bitwise operator hooks can return anything you like. ~custom_obj will evaluate to whatever type(custom_obj).__invert__(custom_obj) returns; custom_obj1 & custom_obj2 will return the result of type(custom_obj1).__and__(custom_obj1, custom_obj2) , unless that method doesn't exist or returns NotImplemented , in which case type(custom_obj2).__rand__(custom_obj2, custom_obj1) is called instead.

Answer 2

not just acts on boolean values in python. If that is sufficient in your use case you can override the __nonzero__ method . Otherwise your stuck to implement your own obj.inverted() method.

Answer 3

>>> hex(~0xaa & 0xff)
'0x55'

Just have to use the matching Python operator.