动态地将基类混入Python中的实例 [英] Dynamically mixin a base class to an instance in Python

问题描述

是否可以在运行时将基类添加到对象实例(不是类！)? Object#extend在Ruby中的工作原理:

Is it possible to add a base class to an object instance (not a class!) at runtime? Something along the lines of how Object#extend works in Ruby:

class Gentleman(object):
  def introduce_self(self):
    return "Hello, my name is %s" % self.name

class Person(object):
  def __init__(self, name):
    self.name = name

p = Person("John")
# how to implement this method?
extend(p, Gentleman)
p.introduce_self() # => "Hello, my name is John"

推荐答案

这动态定义了一个新的类GentlePerson，并为它重新分配了p的类:

This dynamically defines a new class GentlePerson, and reassigns p's class to it:

class Gentleman(object):
  def introduce_self(self):
    return "Hello, my name is %s" % self.name

class Person(object):
  def __init__(self, name):
    self.name = name

p = Person("John")
p.__class__ = type('GentlePerson',(Person,Gentleman),{})
print(p.introduce_self())
# "Hello, my name is John"

根据您的请求，这会修改p的基数，但不会更改p的原始类Person.因此，Person的其他实例不受影响(如果调用introduce_self，则会引发AttributeError).

Per your request, this modifies p's bases, but does not alter p's original class Person. Thus, other instances of Person are unaffected (and would raise an AttributeError if introduce_self were called).

尽管在问题中并未直接询问，但我将为Googlers和好奇心求助者补充说，也可以动态更改类的基础，但是(AFAIK)仅在该类不直接继承自object的情况下:

Although it was not directly asked in the question, I'll add for googlers and curiosity seekers, that it is also possible to dynamically change a class's bases but (AFAIK) only if the class does not inherit directly from object:

class Gentleman(object):
  def introduce_self(self):
    return "Hello, my name is %s" % self.name

class Base(object):pass
class Person(Base):
  def __init__(self, name):
    self.name = name

p = Person("John")
Person.__bases__=(Gentleman,object,)
print(p.introduce_self())
# "Hello, my name is John"

q = Person("Pete")
print(q.introduce_self())
# Hello, my name is Pete

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