基于 Flask 的 Web 应用开发指南

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Flask Web 开发指南 Flask 是一个基于 Python 的微型 web 框架，主要用于构建 web 应用程序。Flask 的主要特点是轻量级、灵活性强、可扩展性好，非常适合中小型 web 项目的开发。 **Flask 的历史** Flask 的开发始于 2010 年，最初由 Armin Ronacher 创建。2014 年，Miguel Grinberg 发布了《Flask Web Development》一书，对 Flask 的功能和使用进行了深入探讨。 **Flask 的特点** 1. 轻量级：Flask 的核心代码只有约 500 行，非常轻量级，易于学习和维护。 2. 灵活性强：Flask 提供了灵活的路由系统、模板引擎和数据库集成功能，能够满足不同级别的开发需求。 3. 可扩展性好：Flask 的插件系统允许开发者轻松地添加新功能，扩展框架的能力。 4. 跨平台支持：Flask 可以在多种平台上运行，包括 Windows、Linux 和 macOS。 **Flask 的应用场景** 1. 中小型 web 项目：Flask 非常适合中小型 web 项目的开发，例如博客、论坛、简单的电商平台等。 2. 快速原型开发：Flask 的轻量级和灵活性使其非常适合快速原型开发和 Proof of Concept（概念证明）。 3. RESTful API 开发：Flask 可以用来开发 RESTful API，提供数据接口给移动应用程序、Web 应用程序或其他服务。 **Flask 的主要组件** 1. 路由系统：Flask 的路由系统允许开发者定义 URL 路由规则，并将其映射到相应的视图函数。 2. 模板引擎：Flask 自带了 Jinja2 模板引擎，允许开发者使用模板来生成动态网页内容。 3. 数据库集成功能：Flask 可以集成多种数据库，例如 SQLite、MySQL、PostgreSQL 等。 **Flask 的优缺点** 优点： * 轻量级，易于学习和维护 * 灵活性强，能够满足不同级别的开发需求 * 可扩展性好，插件系统允许轻松地添加新功能缺点： * 不适合大型复杂项目的开发 * 需要开发者自己实现一些功能，例如身份验证和权限管理 **Flask 的发展前景** Flask 的发展前景非常广阔，随着 Python 的普及和 web 开发技术的演进，Flask 将继续受到开发者的欢迎和青睐。同时，Flask 的插件系统和社区支持也将继续扩展和完善，满足开发者的需求。

The git clone command installs the source code from GitHub into a flasky folder that

is created in the current directory. This folder does not contain just source code; a copy

of the Git repository with the entire history of changes made to the application is also

included.

In the first chapter you will be asked to check out the initial release of the application,

and then, at the proper places you will be instructed to move forward in the history.

The Git command that lets you move through the change history is git checkout. Here

is an example:

$ git checkout 1a

The 1a referenced in the command is a tag, a named point in the history of the project.

This repository is tagged according to the chapters of the book, so the 1a tag used in

the example sets the application files to the initial version used in Chapter 1. Most

chapters have more than one tag associated with them, so, for example, tags 5a, 5b, and

so on are incremental versions presented in Chapter 5.

In addition to checking out the source files for a version of the application, you may

need to perform some setup. For example, in some cases you will need to install addi‐

tional Python packages or apply updates to the database. You will be told when these

are necessary.

You will normally not modify the source files of the application, but if you do, then Git

will not let you check out a different revision, as that would cause your local changes to

be lost. Before you can check out a different revision, you will need to revert the files to

their original state. The easiest way to do this is with the git reset command:

$ git reset --hard

This command will destroy your local changes, so you should save anything you don’t

want to lose before you use this command.

From time to time, you may want to refresh your local repository from the one on

GitHub, where bug fixes and improvements may have been applied. The commands

that achieve this are:

$ git fetch --all

$ git fetch --tags

$ git reset --hard origin/master

The git fetch commands are used to update the commit history and the tags in your

local repository from the remote one on GitHub, but none of this affects the actual

source files, which are updated with the git reset command that follows. Once again,

be aware that any time git reset is used you will lose any local changes you have made.

Another useful operation is to view all the differences between two versions of the

application. This can be very useful to understand a change in detail. From the command

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line, the git diff command can do this. For example, to see the difference between

revisions 2a and 2b, use:

$ git diff 2a 2b

The differences are shown as a patch, which is not a very intuitive format to review

changes if you are not used to working with patch files. You may find that the graphical

comparisons shown by GitHub are much easier to read. For example, the differences

between revisions 2a and 2b can be viewed on GitHub at https://github.com/miguelgrin

berg/flasky/compare/2a...2b

Using Code Examples

This book is here to help you get your job done. In general, if example code is offered

with this book, you may use it in your programs and documentation. You do not need

to contact us for permission unless you’re reproducing a significant portion of the code.

For example, writing a program that uses several chunks of code from this book does

not require permission. Selling or distributing a CD-ROM of examples from O’Reilly

books does require permission. Answering a question by citing this book and quoting

example code does not require permission. Incorporating a significant amount of ex‐

ample code from this book into your product’s documentation does require permission.

We appreciate, but do not require, attribution. An attribution usually includes the title,

author, publisher, and ISBN. For example: “Flask Web Development by Miguel Grinberg

If you feel your use of code examples falls outside fair use or the permission given above,

feel free to contact us at permissions@oreilly.com.

Conventions Used in This Book

The following typographical conventions are used in this book:

Italic

Indicates new terms, URLs, email addresses, filenames, and file extensions.

Constant width

Used for program listings, as well as within paragraphs to refer to program elements

such as variable or function names, databases, data types, environment variables,

statements, and keywords.

Constant width bold

Shows commands or other text that should be typed literally by the user.

Preface | xv

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How to Contact Us

Please address comments and questions concerning this book to the publisher:

O’Reilly Media, Inc.

1005 Gravenstein Highway North

Sebastopol, CA 95472

800-998-9938 (in the United States or Canada)

707-829-0515 (international or local)

707-829-0104 (fax)

We have a web page for this book, where we list errata, examples, and any additional

information. You can access this page at http://www.bit.ly/flask-web-dev.

To comment or ask technical questions about this book, send email to bookques

tions@oreilly.com.

For more information about our books, courses, conferences, and news, see our website

at http://www.oreilly.com.

Find us on Facebook: http://facebook.com/oreilly

Watch us on YouTube: http://www.youtube.com/oreillymedia

Acknowledgments

I could not have written this book alone. I have received a lot of help from family, co-

workers, old friends, and new friends I’ve made along the way.

I’d like to thank Brendan Kohler for his detailed technical review and for his help in

giving shape to the chapter on Application Programming Interfaces. I’m also in debt to

David Baumgold, Todd Brunhoff, Cecil Rock, and Matthew Hugues, who reviewed the

manuscript at different stages of completion and gave me very useful advice regarding

what to cover and how to organize the material.

Writing the code examples for this book was a considerable effort. I appreciate the help

of Daniel Hofmann, who did a thorough code review of the application and pointed out

several improvements. I’m also thankful to my teenage son, Dylan Grinberg, who sus‐

pended his Minecraft addiction for a few weekends and helped me test the code under

several platforms.

O’Reilly has a wonderful program called Early Release that allows impatient readers to

have access to books while they are being written. Some of my Early Release readers

went the extra mile and engaged in useful conversations regarding their experience

working through the book, leading to significant improvements. I’d like to acknowledge

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