python根据类名映射

dog.py
class Dog:
        def __init__(self,name):
                self._name = name
        def run(self):
                print 'wang wang,i am '+self._name

test.py
import dog

#使用eval
class_name = 'dog.Dog'
a_dog = eval(class_name+"('a dog')")
a_dog.run()

#使用动态导入
a_class = getattr(dog,'Dog')
b_dog = a_class('b dog')
b_dog.run()