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Creando objetos de método definidos por el usuario

Los objetos de método definidos por el usuario pueden crearse cuando se obtiene un atributo de una clase (quizás a través de una instancia de esa clase), si ese atributo es un objeto de función definido por el usuario, un objeto de método definido por el usuario no vinculado o un objeto de método de clase.

class A(object):
    # func: A user-defined function object
    #
    # Note that func is a function object when it's defined,
    # and an unbound method object when it's retrieved.
    def func(self): 
        pass

    # classMethod: A class method
    @classmethod
    def classMethod(self):
        pass

class B(object):
    # unboundMeth: A unbound user-defined method object
    #
    # Parent.func is an unbound user-defined method object here,
    # because it's retrieved.
    unboundMeth = A.func

a = A()
b = B()

print A.func
# output: <unbound method A.func>
print a.func
# output: <bound method A.func of <__main__.A object at 0x10e9ab910>>
print B.unboundMeth
# output: <unbound method A.func>
print b.unboundMeth
# output: <unbound method A.func>
print A.classMethod
# output: <bound method type.classMethod of <class '__main__.A'>>
print a.classMethod
# output: <bound method type.classMethod of <class '__main__.A'>>

Cuando el atributo es un objeto de método definido por el usuario, un nuevo objeto de método solo se crea si la clase de la cual se está recuperando es la misma clase que la clase almacenada en el objeto de método original, o una clase derivada de la misma; de lo contrario, el objeto del método original se usa tal como es.

# Parent: The class stored in the original method object
class Parent(object):
    # func: The underlying function of original method object
    def func(self): 
        pass
    func2 = func

# Child: A derived class of Parent
class Child(Parent):
    func = Parent.func

# AnotherClass: A different class, neither subclasses nor subclassed
class AnotherClass(object):
    func = Parent.func
    
print Parent.func is Parent.func                # False, new object created
print Parent.func2 is Parent.func2              # False, new object created
print Child.func is Child.func                  # False, new object created
print AnotherClass.func is AnotherClass.func    # True, original object used

Ejemplo de tortuga

El siguiente es un ejemplo del uso de una función definida por el usuario para ser llamada varias veces (∞) en un script con facilidad.

import turtle, time, random #tell python we need 3 different modules
turtle.speed(0) #set draw speed to the fastest 
turtle.colormode(255) #special colormode
turtle.pensize(4) #size of the lines that will be drawn
def triangle(size): #This is our own function, in the parenthesis is a variable we have defined that will be used in THIS FUNCTION ONLY. This fucntion creates a right triangle
    turtle.forward(size) #to begin this function we go forward, the amount to go forward by is the variable size
    turtle.right(90) #turn right by 90 degree
    turtle.forward(size) #go forward, again with variable
    turtle.right(135) #turn right again
    turtle.forward(size * 1.5) #close the triangle. thanks to the Pythagorean theorem we know that this line must be 1.5 times longer than the other two(if they are equal)
while(1): #INFINITE LOOP
    turtle.setpos(random.randint(-200, 200), random.randint(-200, 200)) #set the draw point to a random (x,y) position
    turtle.pencolor(random.randint(1, 255), random.randint(1, 255), random.randint(1, 255)) #randomize the RGB color
    triangle(random.randint(5, 55)) #use our function, because it has only one variable we can simply put a value in the parenthesis. The value that will be sent will be random between 5 - 55, end the end it really just changes ow big the triangle is.
    turtle.pencolor(random.randint(1, 255), random.randint(1, 255), random.randint(1, 255)) #randomize color again


Modified text is an extract of the original Stack Overflow Documentation
Licenciado bajo CC BY-SA 3.0
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