学习 Flask Web Development 2nd Edition

Posted 2021-04-12 加载Python技能

学习思想：学习可以看作一个 输入-方法-输出 过程，敲几遍是 Learn by Doing 的实践，是一种有效的方式目标：学习 Flask Web Development 2nd Edition环境：Python 3.6.4, Flask

前言 (Preface) 查看示例代码

$git clone https://github.com/miguelgrinberg/flasky.git

进入 flasky 目录

$cd flasky

进入某一个 commit 历史，比如 1a 这个 tag

$git checkout 1a

如果有什么改动，用 git checkout 进入下一个标签会失败，用 git reset 命令可以还原任何改变。所以如果在使用这个命令前，不想丢失某些改变，应该 git commit 做保存

$git reset --hard

如果想要更新（刷新）本地的仓库，和 github 上的仓库保持一致，可以用这几个命令

$git fetch --all
$git fetch --tags
$git reset --hard origin/master

git diff 命令可以显示出不同版本的不同之处，比如，查看 2a 和 2b 版本的不同可以用这个命令

$git diff 2a 2b

第一章 安装 (Installation)

如果你自己敲代码，不只是看克隆的代码，可以新建一个空文件夹

$mkdir flaksy
$cd flasky

创建一个 Python 3 的虚拟环境，我这里已经安装了 pipenv，就用这个命令

$pipenv shell

用 pipenv 安装 Python Packages，在虚拟环境下安装 Flask 包，用这个命令

pipenv install flask

确认 Flask 已经安装就绪，用 Python 解释器查看

$python
>>>import flask
>>>

第二章 应用的基本结构 （Basic Application Structure）

Flask 应用都要创建应用实例。应用实例是一个 Flask 类的对象，通常这样创建

from flask import Flask
app = Flask(__name__)

路由 (route) 可以关联 URL 和 Python 函数 (function). 最方便的定义路由的方式是用 app.route 装饰器，比如

@app.route('/')
def index():
    return '<h1>Hello World!</h1>'

Flask 有一个传统的方式设置路由，用 app.add_url_rule() 方法，有三个基本参数，URL，endpoint 名字，view 函数，下面是一个等价写法

def index():
    return '<h1>Hello World!</h1>'
app.add_url_rule('/', 'index', index)    

index() 就是一个 view 函数路由可以包含变量部分，使用 app.route 装饰器，包含在 <> 内，比如

@app.route('/user/<name>')
def user(name):
    return '<h1>Hello, {}!</h1>'.format(name)

Flask 支持的路由变量部分的类型包括 string, int, float 和 path, path 类型是可以包含 / 的特殊 string. 比如，变量部分是整数，/user/<int:id>把应用实例、路由和 view 函数放到一起，就成为一个完整的 Flask 应用

# hello.py
from flask import Flask
app = Flask(__name__)

@app.route('/')
def index():
    return '<h1>Hello World!</h1>'

用 flask run 可以运行开发的 Flask 应用。

$export FLASK_APP=hello.py
$flask run

用浏览器打开 http://127.0.0.1:5000/ 可以看到这个页面增加一个动态路由

# hello.py
from flask import Flask
app = Flask(__name__)

@app.route('/')
def index():
    return '<h1>Hello World!</h1>'

@app.route('/user/<name>')
def user(name):
    return '<h1>Hello, {}!</h1>'.format(name)

sever 继续运行，可以到 http://localhost:5000/user/sam 测试动态路由开发阶段，debug 模式很有用，因为 reloader 模块可以在代码修改后自动重启 server，debugger 模块可以让我们在浏览器查看 exception 信息。但是 debug 模式是默认关闭的，可以在调用 flask run 之前设置FLASK_DEBUG=1

$export FLASK_APP=hello.py
$export FLASK_DEBUG=1
$flask run

命令行选项

$flask --help

$flask run --help

$flask run --host 0.0.0.0

request-response 循环

from flask import request

@app.route('/')
def index():
    user_agent = request.headers.get('User-Agent')
    return '<p>Your browser is {}</p>'.format(user_agent)

Flask 有两种环境 (conntexts): application context 和 request context

Variable name	Context	Description
current_app	Application context	The application instance for the active application.
g	Application context	An object that the application can use for temporary storage during the handling of a request. This variable is reset with each request.
request	Request context	The request object, which encapsulates the contents of a HTTP request sent by the client.
session	Request context	The user session, a dictionary that the application can use to store values that are “remembered” between requests. This object will be

示例一下 applicaiton context 是如何工作的

>>> from hello import app
>>> from flask import current_app
>>> current_app.name
Traceback (most recent call last):
...
RuntimeError: working outside of application context
>>> app_ctx = app.app_context()
>>> app_ctx.push()
>>> current_app.name
'hello'
>>> app_ctx.pop()

request 派遣 (Request Dispatching)

>>> from hello import app
>>> app.url_map
Map([<Rule '/' (HEAD, OPTIONS, GET) -> index>,
 <Rule '/static/<filename>' (HEAD, OPTIONS, GET) -> static>,
 <Rule '/user/<name>' (HEAD, OPTIONS, GET) -> user>])

最常用的 Flask request 对象 (object)

Attribute or Method	Description
form	A dictionary with all the form fields submitted with the request.
args	A dictionary with all the arguments passed in the query string of the URL.
values	A dictionary that combines the values in form and args.
cookies	A dictionary with all the cookies included in the request.
headers	A dictionary with all the HTTP headers included in the request.
files	A dictionary with all the file uploads included with the request.
get_data()	Return the buffered data from the request body.
get_json()	A Python dictionary with the parsed JSON included in the body of the request.
blueprint	The name of the Flask blueprint that is handling the request.
endpoint	The name of the Flask endpoint that is handling the request. Flask uses the name of the view function as the endpoint name for a route.
method	The HTTP request method, such as GET or POST.
scheme	The URL scheme (http or https).
is_secure()	Return True if the request came through a secure (https) connection.
host	The host defined in the request, including the port number if given by the client.
path	The path portion of the URL.
query_string	The query string portion of the URL, as a raw binary value.
full_path	The path and query string portions of the URL.
url	The complete URL requested by the client.
base_url	Same as url, but without the query string component.
remote_addr	The IP address of the client.
environ	The raw WSGI environment dictionary for the request.

Request 挂钩 (Request Hooks)Request 挂钩以装饰器实现，Flask 支持四种 Request 挂钩：before_first_request, before_request, after_request,teardown_request响应 (Responses)view 函数返回一个状态 400 代码示例

@app.route('/')
def index():
    return '<h1>Bad Request</h1>', 400

响应对象 (response object) 示例

from flask import make_response

@app.route('/')
def index():
    response = make_response('<h1>This document carries a cookie!</h1>')
    response.set_cookie('answer', '42')
    return response

最常用的 Flask Response Object (响应对象)

Attribute or Method	Description
status_code	The numeric HTTP status code.
headers	A dictionary-like object with all the headers that will be sent with the response.
set_cookie()	Add a cookie to the response.
delete_cookie()	Remove a cookie.
content_length	The length of the response body.
content_type	The media type of the response body.
set_data()	Set the response body as a string or bytes value.
get_data()	Get the response body.

一种特殊的响应 redirect() 示例

from flask import redirect

@app.route('/')
def index():
    return redirect('http://www.example.com')

一种特殊的响应 abort() 示例

from flask import abort

@app.route('/user/<id>')
def get_user(id):
    user = load_user(id)
    if not user:
        abort(404)
    return '<h1>Hello, {}</h1>'.format(user.name)