Python 如何使用'functools.partial（）向类动态添加方法`

在以下情况下，使用

functools.partial

将动态方法添加到类中时，我遇到了正确的咒语问题。下面有一个

Creator

类，我想向其中添加一个

create\u someclass

方法，该方法由

Creator

类状态部分参数化

import functools

class Creator:
    def __init__(self, params):
        self.params = params

class Stitch:
    __tablename__ = 'stitch'
    def __init__(self, params, name):
        self.name = name
        self.params = params

def create(self, clz, *args, **kwargs):
    return clz(self.params, *args, **kwargs)

for clazz in [Stitch]:
    setattr(Creator, 'create_%s' % clazz.__tablename__, functools.partial(create, clz=clazz))

creator = Creator('params')

# Neither of these work, but I'd like either one -- preferably the first one.

stitch = creator.create_stitch('myname')
# AttributeError: 'str' object has no attribute 'params'

stitch = creator.create_stitch(name='myname')  
# TypeError: create() missing 1 required positional argument: 'self'

---

对于类方法来说，这是一个问题，因此在Python3.4中我们引入了

partialmethod

。其工作方式如下：

import functools

class Creator:
    def __init__(self, params):
        self.params = params

class Stitch:
    __tablename__ = 'stitch'
    def __init__(self, params, name):
        self.name = name
        self.params = params

def create(self, clz, *args, **kwargs):
    return clz(self.params, *args, **kwargs)

for clazz in [Stitch]:
    setattr(Creator, 'create_%s' % clazz.__tablename__, functools.partialmethod(create, clz=clazz))
    # use partialmethod instead here

creator = Creator('params')

stitch = creator.create_stitch(name='myname')  
# works!

---

我认为问题在于

create

是Stitch的一个成员函数（尽管缩进不好：

create

访问

Stitch

的成员变量

params

），因此需要

Stitch

类型的对象才能与

create

一起使用，然后，它也将作为第一个参数传递给

create

。它的工作原理如下：

import functools


class Creator:
    def __init__(self, params):
        self.params = params

class Stitch:
    __tablename__ = 'stitch'
    def __init__(self, params, name):
        self.name = name
        self.params = params

    def create(self, clz, *args, **kwargs):
        return clz(self.params, *args, **kwargs)


creator = Creator('params')
stitch1 = Stitch('pp', 'my_name')
print("stitch1= ", stitch1)

for clazz in [Stitch]:
    setattr(Creator, 'create_%s' % clazz.__tablename__, functools.partial(stitch1.create, clazz))

stitch = creator.create_stitch('myname')
print("stitch= ", stitch)