Python Language Hacer clases personalizables ordenable


Ejemplo

min , max y sorted todos necesitan que los objetos se puedan ordenar. Para ser ordenados adecuadamente, la clase necesita definir todos los 6 métodos __lt__ , __gt__ , __ge__ , __le__ , __ne__ y __eq__ :

class IntegerContainer(object):
    def __init__(self, value):
        self.value = value
        
    def __repr__(self):
        return "{}({})".format(self.__class__.__name__, self.value)
    
    def __lt__(self, other):
        print('{!r} - Test less than {!r}'.format(self, other))
        return self.value < other.value
    
    def __le__(self, other):
        print('{!r} - Test less than or equal to {!r}'.format(self, other))
        return self.value <= other.value

    def __gt__(self, other):
        print('{!r} - Test greater than {!r}'.format(self, other))
        return self.value > other.value

    def __ge__(self, other):
        print('{!r} - Test greater than or equal to {!r}'.format(self, other))
        return self.value >= other.value

    def __eq__(self, other):
        print('{!r} - Test equal to {!r}'.format(self, other))
        return self.value == other.value

    def __ne__(self, other):
        print('{!r} - Test not equal to {!r}'.format(self, other))
        return self.value != other.value

Aunque implementar todos estos métodos parece innecesario, omitir algunos de ellos hará que su código sea propenso a errores .

Ejemplos:

alist = [IntegerContainer(5), IntegerContainer(3),
         IntegerContainer(10), IntegerContainer(7)
        ]

res = max(alist)
# Out: IntegerContainer(3) - Test greater than IntegerContainer(5)
#      IntegerContainer(10) - Test greater than IntegerContainer(5)
#      IntegerContainer(7) - Test greater than IntegerContainer(10)
print(res)
# Out: IntegerContainer(10)

res = min(alist)   
# Out: IntegerContainer(3) - Test less than IntegerContainer(5)
#      IntegerContainer(10) - Test less than IntegerContainer(3)
#      IntegerContainer(7) - Test less than IntegerContainer(3)
print(res)
# Out: IntegerContainer(3)

res = sorted(alist)
# Out: IntegerContainer(3) - Test less than IntegerContainer(5)
#      IntegerContainer(10) - Test less than IntegerContainer(3)
#      IntegerContainer(10) - Test less than IntegerContainer(5)
#      IntegerContainer(7) - Test less than IntegerContainer(5)
#      IntegerContainer(7) - Test less than IntegerContainer(10)
print(res)
# Out: [IntegerContainer(3), IntegerContainer(5), IntegerContainer(7), IntegerContainer(10)]

sorted con reverse=True también usa __lt__ :

res = sorted(alist, reverse=True)
# Out: IntegerContainer(10) - Test less than IntegerContainer(7)
#      IntegerContainer(3) - Test less than IntegerContainer(10)
#      IntegerContainer(3) - Test less than IntegerContainer(10)
#      IntegerContainer(3) - Test less than IntegerContainer(7)
#      IntegerContainer(5) - Test less than IntegerContainer(7)
#      IntegerContainer(5) - Test less than IntegerContainer(3)
print(res)
# Out: [IntegerContainer(10), IntegerContainer(7), IntegerContainer(5), IntegerContainer(3)]

Pero sorted puede usar __gt__ cambio si el valor predeterminado no está implementado:

del IntegerContainer.__lt__   # The IntegerContainer no longer implements "less than"

res = min(alist) 
# Out: IntegerContainer(5) - Test greater than IntegerContainer(3)
#      IntegerContainer(3) - Test greater than IntegerContainer(10)
#      IntegerContainer(3) - Test greater than IntegerContainer(7)
print(res)
# Out: IntegerContainer(3)

Los métodos de clasificación generarán un TypeError si no se implementan __lt__ ni __gt__ :

del IntegerContainer.__gt__   # The IntegerContainer no longer implements "greater then"

res = min(alist) 

TypeError: tipos no ordenados: IntegerContainer () <IntegerContainer ()


functools.total_ordering decorador functools.total_ordering se puede utilizar para simplificar el esfuerzo de escribir estos métodos de comparación ricos. Si total_ordering tu clase con total_ordering , necesitas implementar __eq__ , __ne__ y solo uno de los __lt__ , __le__ , __ge__ o __gt__ , y el decorador completará el resto:

import functools

@functools.total_ordering
class IntegerContainer(object):
    def __init__(self, value):
        self.value = value
        
    def __repr__(self):
        return "{}({})".format(self.__class__.__name__, self.value)
    
    def __lt__(self, other):
        print('{!r} - Test less than {!r}'.format(self, other))
        return self.value < other.value
    
    def __eq__(self, other):
        print('{!r} - Test equal to {!r}'.format(self, other))
        return self.value == other.value
    
    def __ne__(self, other):
        print('{!r} - Test not equal to {!r}'.format(self, other))
        return self.value != other.value


IntegerContainer(5) > IntegerContainer(6)
# Output: IntegerContainer(5) - Test less than IntegerContainer(6)
# Returns: False

IntegerContainer(6) > IntegerContainer(5)
# Output: IntegerContainer(6) - Test less than IntegerContainer(5)
# Output: IntegerContainer(6) - Test equal to IntegerContainer(5)
# Returns True

Observe cómo el > ( mayor que ) ahora llama al método menos que , y en algunos casos incluso el método __eq__ . Esto también significa que si la velocidad es de gran importancia, debe implementar cada método de comparación enriquecida.