思路:
用一个字典存储beanName和资源
初始化时先将beanName和资源注册到字典中
然后用一个Dscriptor类根据beanName动态请求资源,从而实现控制反转
# -*- coding:utf-8 -*-
import os
class BeanFactory:
"""
Python版控制反转
context: 存储bean的名字和对应的类或者值的字典
allowRepalce: 是否允许替换已经注入的bean
"""
def __init__(self,allowReplace=False):
"""构造函数
allowReplace:是否允许替换已经注入的bean
"""
self.context = {}
self.allowReplace = allowReplace
def setBean(self,beanName,resource,*args,**kwargs):
if not self.allowReplace:
assert not beanName in self.context,"该BeanFactory不允许重复注入%r,请修改beanName" % beanName
def call():
"""定义一个函数闭包,如果注入的resource是可调用类型,就将*args和**kwargs传入并调用该函数,然后将返回值返回
如果是一个不可调用对象,就直接返回
"""
if callable(resource):
return resource(*args,**kwargs)
else:
return resource
#将call闭包与beanName建立映射
self.context[beanName]=call
def __getitem__(self,beanName):
"""重载__getitem__方法,使得BeanFactory支持使用[]获取beanName对应的注册的资源
"""
try:
# 从context字典中取出beanName对应的资源
resource = self.context[beanName]
except KeyError:
raise KeyError("%r 未注册" % beanName)
# 返回闭包函数调用后的结果
return resource()
AppFactory = BeanFactory()
def NoAssertion(obj): return True
def IsInstanceOf(*classes):
def test(obj): return isinstance(obj, classes)
return test
def HasAttributes(*attributes):
def test(obj):
for each in attributes:
if not hasattr(obj, each): return False
return True
return test
def HasMethods(*methods):
def test(obj):
for each in methods:
try:
attr = getattr(obj, each)
except AttributeError:
return False
if not callable(attr): return False
return True
return test
#
#
#Descriptor就是一类实现了__get__(), __set__(), __delete__()方法的对象
#若一个类的成员是descriptor,在访问它的值时是通过__get__()函数访问的
#用这个特性实现在访问一个类的成员时自动到BeanFactory中请求对应的资源
class RequiredResource(object):
def __init__(self, beanName, assertion=NoAssertion):
self.beanName = beanName
self.assertion = assertion
def __get__(self, obj, T):#每次访问descriptor时都会调用__get__方法
return self.result # <-- .操作符会自动调用__getattr__
def __getattr__(self, name):
assert name == 'result', "Unexpected attribute request other then 'result'"
self.result = self.Request()
return self.result
def Request(self):
obj = AppFactory[self.beanName]
assert self.assertion(obj),
"The value %r of %r does not match the specified criteria"
% (obj, self.feature)
return obj
class Component(object):
"Symbolic base class for components"
class Bar(Component):
# HasMethods是一个闭包函数,传入RequiredResource后用于检查'Console'
# 对应的注册的那个feature是否有'WriteLine'方法
# IsinstanceOf(str) 是一个闭包,传入RequiredResource后会被调用,用于
# 检查注册的'AppTitle'对应资源是否是一个字符串
# IsinstanceOf(str) 是一个闭包,传入RequiredResource后会被调用,用于
# 检查'CurrentUser'对应的资源是否是一个字符串
# RequiredFeatuire是desciptor,每次访问descriptor（即实现了__get__的类），都会先经过__get__函数。
con = RequiredResource('Console', HasMethods('WriteLine'))
title = RequiredResource('AppTitle', IsInstanceOf(str))
user = RequiredResource('CurrentUser', IsInstanceOf(str))
flist = RequiredResource('show_dir',IsInstanceOf(list))
def __init__(self):
self.X = 0
def PrintYourself(self):
self.con.WriteLine('-- Bar instance --')
# title 由 RequiredResource('AppTitle',IsInstanceOf(str))生成
#'AppTitle'对应的值在__main__代码块注册了一个值
self.con.WriteLine('Title: %s' % self.title)
self.con.WriteLine('User: %s' % self.user)
self.con.WriteLine('X: %d' % self.X)
for f in self.flist:
self.con.WriteLine(f)
class BetterConsole(Component):
def __init__(self, prefix=''):
self.prefix = prefix
def WriteLine(self, s):
lines = s.split('
')
for line in lines:
if line:
print(self.prefix, line)
else:
print
def GetCurrentUser():
return os.getenv('USERNAME') or 'Some User' # USERNAME is platform-specific
def ShowDir():
return os.listdir()
if __name__ == '__main__':
print('
*** IoC Demo ***')
#Provide(feature,provider,*args,**kwargs) feature是要生成的对象的父类类型 provider是要注入的子类或者值
AppFactory.setBean('AppTitle', 'Inversion of Control ...
... The Python Way')
AppFactory.setBean('CurrentUser', GetCurrentUser)
AppFactory.setBean('Console', BetterConsole, prefix='-->') # <-- transient lifestyle
AppFactory.setBean('show_dir',ShowDir)
bar = Bar()
bar.PrintYourself()