渐进式网络应用程序, 英文名: Progressive Web App, 简称 PWA。 亲爹 - google，目前已经得到 Microsoft，Apple， Firefox 等大厂的支持，特别 Microsoft 更加激进直接将 PWA 应用设置为其应用商店的一等公民，而且必应爬虫找到符合质量的 PWA 应用直接加到应用商店。

Identity, equality and aliases

In python, every object has an identity, a type and a value. An object’s identity never changes once it has been created; you may think of it as the object’s address in memory. The is operator compares the identify of two objects; the id() function returns an integer representing its identify. The real meaning of an object’s id is implementation-dependent.

Decorators

A decorator is a callable that takes another functions as argument (the decorated function). The decorator may perform some processing with the decorated function, and returns it or repalces it with another function or callable object.

First-class Objects

Functions in python area first-class objects:

• created at runtime
• assigned to a variable or element in a data structure
• passed as an argument to function
• returned as the result of a function

Character issues

The concept of “string” is simple enough: a string is a sequence of characters. In python 3 str are Unicode character, just like the items of a unicode object in python 2, while in python 2 str are the raw bytes.