python 类工厂

# 创建工厂类函数

def create_animal_class():

    def init(self,name):
        self.name = name

    def eat(self):
        pass

    def go_to_vet(self):
        pass

    return type('Animal',(object,),{
        '__doc__': "a class representing an animal", '__init__': init,
        'eat': eat, 'go_to_vet': go_to_vet
    })

animal1 = create_animal_class()
animal2 = create_animal_class()
print(animal1 == animal2)

def creat_animal_classes():

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

        def eat(self):
            pass

        def go_to_vet(self):
            pass

    return Animal

class C(object):

    foo = 'bar'

    @classmethod
    def classfoo(cls):
        return cls.foo


#关于单例模式（让类工厂返回类的实例，而不是返回类）
def CPrime(new_foo='bar'):

    if new_foo == 'bar':
        return C()

    class SubC(C):
        foo = new_foo
    return SubC()

cprime = CPrime('foo')
print(cprime)
cprime = CPrime('foo1')
print(cprime)

# 上述方式存在的问题：很多类需要将参数发送给__init__方法，此时该函式就无法处理这种情况

import csv
from django import forms

def CredentialForm(service,*args,**kwargs):
    "返回类实例"
    keys = []

    with open('creds.csv','r') as csvfile:
        for row in csv.reader(csvfile):
            if row[0].lower() != service.lower():
                continue

            keys.append(row[1])

    attrs = {}
    for key in keys:
        field_kw = {}
        if key == 'password':
            field_kw['widget'] = forms.PasswordInput

        attrs[key] = forms.CharField(**field_kw)

    metaclass = type(forms.Form)

    cls = metaclass('CredentialForm',(forms.Form,),attrs)
    return cls(*args,**kwargs)