反射：
getattr(obj,'xxx')
导入模块：
import re
'django.middleware.clickjacking.XFrameOptionsMiddleware'
m = importlib.import_module('django.middleware.clickjacking')
cls = getattr(m,'XFrameOptionsMiddleware')
cls()
面向对象：
#示例一: 之后爬虫使用
class Foo:
def __init__(self):
pass
@classmethod
def instance(cls):
return cls()
def process(self):
pass
if hasattr(Foo,'instance'):
obj = Foo.instance()
else:
obj = Foo()
obj.process()
#示例二:
class A:
def f1(self)：
self.f2()
def f2(self):
print('A.f2')
class B(A):
def f2(self):
print("B.f2")
obj = B()
obj.f1()
