Python入门基础知识（二）

一、构建一个Web应用

除了已经掌握的python知识，要构建一个实际运行的服务器端Web应用，还需要了解Web应用框架，它提供了一组通用的基础技术，可以基于这些技术构建你的Web应用，在这里，我们直接选择一个名为Flask的流行框架

安装Flask
windows上，打开一个命令行提示窗口，一定要作为管理员运行，执行下面的命令：

py -3 -m pip install flask

在Mac OS或Linux上，在一个终端窗口键入以下命令：

sudo -H python3 -m pip install flask

检查Flask是否已经安装并正常运行

from flask import Flask

app = Flask(__name__)

@app.route('/')
def hello() -> str:
    return 'Hello world from Flask!'

app.run()

保存这段程序命名为hello_flask.py
在windows命令窗口下运行这段程序：

py -3 hello_flask.py

在浏览器中输入127.0.0.1:5000,若显示Hello world from Flask!则运行成功啦

构建HTML表单，为Web提供功能

具体的HTML代码和css样式，
戳这儿：https://github.com/wentaoStyle/HeadFirstPython/tree/master/ch4

from flask import Flask, render_template, request
from vsearch import search4letters

app = Flask(__name__)


@app.route('/search4', methods=['POST'])
def do_search() -> 'html':
    phrase = request.form['phrase']
    letters = request.form['letters']
    title = 'Here are your results:'
    results = str(search4letters(phrase, letters))
    return render_template('results.html',
                           the_title=title,
                           the_phrase=phrase,
                           the_letters=letters,
                           the_results=results,)


@app.route('/')
@app.route('/entry')
def entry_page() -> 'html':
    return render_template('entry.html',
                           the_title='Welcome to search4letters on the web!')


if __name__ == '__main__':
    app.run(debug=True)

小插曲：
HTTP的5类状态码：
100-199范围内的状态码是信息消息，这些状态码都没有问题，服务器在提供关于客户端请求的详细信息
200-299范围内的状态码是成功消息：服务器已经接收、理解和处理客户端的请求。一切正常。
300-399范围内的状态码是重定向消息：服务器通知客户端请求在别处处理。
400-499范围内的状态码是客户端错误消息：服务器从客户端接收到一个他不理解也无法处理的请求。通常这是客户端的问题。
500-599范围内的状态码是服务器端错误消息：服务器从客户端接收一个请求，但是服务器尝试处理这个请求时失败了。通常这是服务器的问题。

二、存储和管理数据

python支持打开、处理和关闭文件

todos = open('todos.txt','a')
print('day day up',file=todos)
todos.close()

tasks = open('todos.txt')
for chore in tasks:
	print(chore,end='')
tasks.close()

with open ('todos.txt') as tasks:
	for chore in tasks:
		print(chore,end='')

with语句用于管理上下文

names = ['l','o','v','e']
python = '|'.join(names)
individuals = pythons.split('|')

from flask import Flask, render_template, request, escape
from vsearch import search4letters

app = Flask(__name__)


def log_request(req: 'flask_request', res: str) -> None:
    with open('vsearch.log', 'a') as log:
        print(req.form, req.remote_addr, req.user_agent, res, file=log, sep='|')


@app.route('/search4', methods=['POST'])
def do_search() -> 'html':
    phrase = request.form['phrase']
    letters = request.form['letters']
    title = 'Here are your results:'
    results = str(search4letters(phrase, letters))
    log_request(request, results)
    return render_template('results.html',
                           the_title=title,
                           the_phrase=phrase,
                           the_letters=letters,
                           the_results=results,)


@app.route('/')
@app.route('/entry')
def entry_page() -> 'html':
    return render_template('entry.html',
                           the_title='Welcome to search4letters on the web!')


@app.route('/viewlog')
def view_the_log() -> 'html':
    contents = []
    with open('vsearch.log') as log:
        for line in log:
            contents.append([])
            for item in line.split('|'):
                contents[-1].append(escape(item))
    titles = ('Form Data', 'Remote_addr', 'User_agent', 'Results')
    return render_template('viewlog.html',
                           the_title='View Log',
                           the_row_titles=titles,
                           the_data=contents,)


if __name__ == '__main__':
    app.run(debug=True)

三、使用数据库

1、安装MySQL服务器
http://dev.mysql.com/downloads/mysql/

2.为python安装一个MySQL数据库驱动程序
http://dev.mysql.com/downloads/connector/python/

3.安装MySQL Connector/Python

py -3 setup.py install

def log_request(req: 'flask_request', res: str) -> None:
    dbconfig = {'host':'127.0.0.1',
                'user':'vsearch',
                'password':'vsearchpasswd',
                'database':'vsearchlogdb',}#定义连接属性
    import mysql.connector#导入数据库驱动程序
    conn = mysql.connector.connect(**dbconfig)#建立与服务器的一个链接
    cursor = conn.cursor()#创建一个游标来想服务器发送命令以及接收结果
    _SQL = """insert into log(phrase,letters,ip,browser_string,results) values
              (%s,%s,%s,%s,%s)"""#将查询赋至一个字符串
    cursor.execute(_SQL,(req.form['phrase'],
                         req.form['letters'],
                         req.remote_addr,
                         req.user_agent.browser,
                         res,))#将查询发送到服务器
    conn.commit()#强制 要求数据库写数据
    cursor.close()
    conn.close()

五、一点点类

class CountFromBy:

    def __init__(self, v:int=0, i:int=1) -> None:
        self.val = v
        self.incr = i

    def increase(self) -> None:
        self.val += self.incr

    def __repr__(self) -> str:
        return str(self.val)

class关键字在代码中引入一个新类
从类创建一个对象看上去非常类似于一个函数调用。

mycount = CountFromBy()

上下文管理协议

import mysql.connector


class UseDatabase:
    def __init__(self, config: dict):
        self.configuration = config
        
               

    def __enter__(self) -> 'cursor':
        self.conn = mysql.connector.connect(**self.configuration)
        self.cursor = self.conn.cursor()
        return self.cursor

    def __exit__(self, exc_type, exc_value, exc_traceback):
        self.conn.commit()
        self.cursor.close()
        self.conn.close()

 with UseDatabase(app.config['dbconfig']) as cursor:
        _SQL = """select phrase, letters, ip, browser_string, results
                  from log"""
        cursor.execute(_SQL)
        contents = cursor.fetchall()

六、函数修饰符

1.函数修饰符是一个函数
2.修饰符取被修饰符为参数
3.修饰符返回一个新函数
4.修饰符维护被修饰函数的签名

创建你自己的修饰符时，一定要导入并使用“functools”模块的"wraps"函数

from flask import session

from functools import wraps

def check_logged_in(func):
    @wraps(func)
    def wrapper(*args, **kwargs):
        if 'logged_in' in session:
            return func(*args, **kwargs)
        return 'You are NOT logged in.'
    return wrapper

七、异常处理

try:
    with open('myfile.txt') as fh:
        file_data = fh.read()
    print(file_data)
except FileNotFoundError:
    print('The data file is missing.')
except PermissionError:
    print('This is not allowed.')
except Exception as err:
    print('Some other error occurred:', str(err))

八、线程

要创建一个线程，你要创建一个Thread对象，将一个名为target的参数指定为你希望这个线程执行的函数名，并为另一个名为args的命名参数提供其他参数（作为一个元组）。再把创建的Thread对象赋给你选择的变量。

from threading import Thread

t = Thread(target=func,arges=())
t.start()

from flask import Flask, render_template, request, escape, session
from vsearch import search4letters

from DBcm import UseDatabase, ConnectionError, CredentialsError, SQLError
from checker import check_logged_in

from threading import Thread
from time import sleep

app = Flask(__name__)

app.config['dbconfig'] = {'host': '127.0.0.1',
                          'user': 'vsearch',
                          'password': 'vsearchpasswd',
                          'database': 'vsearchlogdb', }


@app.route('/login')
def do_login() -> str:
    session['logged_in'] = True
    return 'You are now logged in.'


@app.route('/logout')
def do_logout() -> str:
    session.pop('logged_in')
    return 'You are now logged out.'


def log_request(req: 'flask_request', res: str) -> None:

    
    sleep(15)  #sleep

    with UseDatabase(app.config['dbconfig']) as cursor:
        _SQL = """insert into log
                  (phrase, letters, ip, browser_string, results)
                  values
                  (%s, %s, %s, %s, %s)"""
        cursor.execute(_SQL, (req.form['phrase'],
                              req.form['letters'],
                              req.remote_addr,
                              req.user_agent.browser,
                              res, ))


@app.route('/search4', methods=['POST'])
def do_search() -> 'html':
    phrase = request.form['phrase']
    letters = request.form['letters']
    title = 'Here are your results:'
    results = str(search4letters(phrase, letters))
    try:
        t = Thread(target=log_request, args=(request, results))
        t.start()
    except Exception as err:
        print('***** Logging failed with this error:', str(err))
    return render_template('results.html',
                           the_title=title,
                           the_phrase=phrase,
                           the_letters=letters,
                           the_results=results,)


@app.route('/')
@app.route('/entry')
def entry_page() -> 'html':
    return render_template('entry.html',
                           the_title='Welcome to search4letters on the web!')


@app.route('/viewlog')
@check_logged_in
def view_the_log() -> 'html':
    try:
        with UseDatabase(app.config['dbconfig']) as cursor:
            _SQL = """select phrase, letters, ip, browser_string, results
                    from log"""
            cursor.execute(_SQL)
            contents = cursor.fetchall()
        titles = ('Phrase', 'Letters', 'Remote_addr', 'User_agent', 'Results')
        return render_template('viewlog.html',
                            the_title='View Log',
                            the_row_titles=titles,
                            the_data=contents,)
    except ConnectionError as err:
        print('Is your database switched on? Error:', str(err))
    except CredentialsError as err:
        print('User-id/Password issues. Error:', str(err))
    except SQLError as err:
        print('Is your query correct? Error:', str(err))
    except Exception as err:
        print('Something went wrong:', str(err))    
    return 'Error'

app.secret_key = 'YouWillNeverGuessMySecretKey'

if __name__ == '__main__':
    app.run(debug=True)

九、高级迭代

推导式比等价的for循环代码执行的更快

列表推导式

destinations = []
for dest in flights.values():
	destinations.append(dest.title())

more_dests = [dest.title() for dest in flights.value()]

字典推导式：

just = {}
for k,v in flights.items():
	if v == 'FREEPORT':
		just[covert2ampm(k)] = v.title()

just2 = {covert2ampm(k):v.title() for k,v in flights.items() if v== 'FREEPORT'}

集合推导式

found = set()
for v invowels:
	if v in message:
		found.add(v)


found2 = { v for v in vowels if v in message}

使用列表推导式的地方都可以使用生成器，会生成同样的结果

for i in (x*3 for x in [1,2,3,4,5]):
	print(i)

生成器一次生成一个数据项，使用生成器的徐变换响应性更好，而使用列表推导式的循环会让你等待

列表推导式是用中括号包围的代码，字典推导是是用大括号包围的代码（有冒号分隔符），集合推导式也是用大括号包围的代码（但没有字典推导式的冒号）

如果发现推导式代码用小括号包围，你看到的是一个生成器（可以装换为一个函数，使用yield根据需要生成数据）

from datetime import datetime
import pprint

def convert2ampm(time24: str) -> str:
    return datetime.strptime(time24, '%H:%M').strftime('%I:%M%p')

with open('buzzers.csv') as data:
    ignore = data.readline()
    flights = {}
    for line in data:
        k, v = line.strip().split(',')
        flights[k] = v

pprint.pprint(flights)
print()

fts = {convert2ampm(k): v.title() for k, v in flights.items()}

pprint.pprint(fts)
print()

when = {dest: [k for k, v in fts.items() if v == dest] for dest in set(fts.values())}

pprint.pprint(when)
print()

在这里插入代码片