Design patterns

引用自：https://zhuanlan.zhihu.com/p/31675841
http://www.aleax.it/gdd_pydp.pdf
Design pattern categories:

1. creational：Singleton ，factory，builder，prototype
   factory：define an interface for creating an object, let subclass to decide which class to initialize.
   builder：desperate the build and show case
   prototype: easy for clone
2. structural：Proxy，
3. behavioral