Flask Web开发第二版：Python Web应用构建

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"Flask Web Development V2 - Developing Web Applications with Python, Second Edition by Miguel Grinberg" 本书《Flask Web Development》第二版是Python web开发领域的重要参考资料，由Miguel Grinberg撰写，旨在帮助读者掌握使用Python和Flask框架构建web应用的技能。Flask是一个轻量级的web框架，因其简洁、灵活的特性，在Python开发者中非常受欢迎。作者Miguel Grinberg是一位知名的Python开发者，他的著作深入浅出，适合初学者和有一定经验的开发者阅读。书中涵盖了以下关键知识点： 1. **Flask基础**：介绍Flask的基本结构，包括如何创建一个基本的web应用，定义路由，以及使用模板和静态文件。同时，讲解了请求和响应对象的工作原理，以及如何处理HTTP请求方法（如GET和POST）。 2. **应用程序结构**：讨论如何组织项目结构，使代码更易于管理和扩展。这包括使用蓝prints进行模块化，以及设置配置来管理环境变量。 3. **数据库集成**：讲解如何使用SQLAlchemy作为ORM（对象关系映射）工具，与Flask集成，创建数据模型，以及执行CRUD操作（创建、读取、更新、删除）。还包括了Flask-SQLAlchemy扩展的使用。 4. **用户认证与会话管理**：介绍如何实现用户注册、登录功能，以及使用会话来跟踪用户状态。书中可能会涵盖基于cookie的身份验证策略和Flask-Login库的使用。 5. **表单处理**：讲解如何使用WTForms库来创建和验证用户输入的表单，防止常见的安全问题，如跨站脚本（XSS）和跨站请求伪造（CSRF）。 6. **错误处理与日志记录**：指导读者如何设置自定义错误页面，以及如何有效地记录和调试应用中的问题。 7. **RESTful API设计**：介绍如何利用Flask构建符合REST原则的API，支持JSON数据交换，以及使用Flask-Restplus等扩展。 8. **单元测试与持续集成**：讲解编写单元测试的重要性，如何使用unittest或pytest进行测试，以及如何结合Travis CI或Jenkins实现持续集成。 9. **部署与扩展**：讨论如何将Flask应用部署到生产环境，如使用Gunicorn和Nginx，以及如何实现应用的水平扩展和负载均衡。 10. **最佳实践与进阶话题**：提供关于性能优化、安全性提升、Docker容器化部署等高级主题的指南。通过这本书，读者不仅可以学习到Flask框架的核心概念，还能了解到构建完整web应用所需的周边技术，从而成为一名合格的Flask开发者。无论是初学者还是希望深入理解Flask的开发者，都能从这本书中获得宝贵的知识。

Chapter 2. Basic Application Structure

In this chapter, you will learn about the different parts of a Flask application. You will also write and run

your first Flask web application.

Initialization

All Flask applications must create an application instance. The web server passes all requests it

receives from clients to this object for handling, using a protocol called Web Server Gateway Interface

(WSGI, pronounced “wiz-ghee”). The application instance is an object of class Flask, usually created

as follows:

from flask import Flask

app = Flask(__name__)

The only required argument to the Flask class constructor is the name of the main module or package

of the application. For most applications, Python’s __name__ variable is the correct value for this

argument.

TIP

The __name__ argument that is passed to the Flask application constructor is a source of confusion

among new Flask developers. Flask uses this argument to determine the location of the application,

which in turn allows it to locate other files that are part of the application, such as images and

templates.

Later you will learn more complex ways to initialize an application, but for simple applications this is all

that is needed.

Routes and View Functions

Clients such as web browsers send requests to the web server, which in turn sends them to the Flask

application instance. The Flask application instance needs to know what code it needs to run for each

URL requested, so it keeps a mapping of URLs to Python functions. The association between a URL

and the function that handles it is called a route.

The most convenient way to define a route in a Flask application is through the app.route decorator

exposed by the application instance. The following example shows how a route is declared using this

decorator:

@app.route('/')

def index():

return '<h1>Hello World!</h1>'

NOTE

Decorators are a standard feature of the Python language. A common use of decorators is to register

functions as handler functions to be invoked when certain events occur.

The previous example registers function index() as the handler for the application’s root URL. While

the app.route decorator is the preferred method to register view functions, Flask also offers a more

traditional way to set up the application routes with the app.add_url_rule() method, which in its most

basic form takes three arguments: the URL, the endpoint name, and the view function. The following

example uses app.add_url_rule() to register an index() function that is equivalent to the one shown

previously:

def index():

return '<h1>Hello World!</h1>'

app.add_url_rule('/', 'index', index)

Functions like index() that handle application URLs are called view functions. If the application is

deployed on a server associated with the www.example.com domain name, then navigating to

http://www.example.com/ in your browser would trigger index() to run on the server. The return value of

this view function is the response the client receives. If the client is a web browser, this response is the

document that is displayed to the user in the browser window. A response returned by a view function

can be a simple string with HTML content, but it can also take more complex forms, as you will see

later.

NOTE

Embedding response strings with HTML code in Python source files leads to code that is difficult to

maintain. The examples in this chapter do it only to introduce the concept of responses. You will learn

a better way to generate HTML responses in Chapter 3.

If you pay attention to how some URLs for services that you use every day are formed, you will notice

that many have variable sections. For example, the URL for your Facebook profile page has the format

https://www.facebook.com/<your-name>, which includes your username, making it different for each

user. Flask supports these types of URLs using a special syntax in the app.route decorator. The

following example defines a route that has a dynamic component:

@app.route('/user/<name>')

def user(name):

return '<h1>Hello, {}!</h1>'.format(name)

The portion of the route URL enclosed in angle brackets is the dynamic part. Any URLs that match the

static portions will be mapped to this route, and when the view function is invoked, the dynamic

component will be passed as an argument. In the preceding example, the name argument is used to

generate a response that includes a personalized greeting.

The dynamic components in routes are strings by default but can also be of different types. For

example, the route /user/<int:id> would match only URLs that have an integer in the id dynamic

segment, such as /user/123. Flask supports the types string, int, float, and path for routes. The path

type is a special string type that can include forward slashes, unlike the string type.

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