Python-web验证码的实现

马哥Python网络班学员问题：能否说下web验证的原理，感觉文字描述不清楚，
此代码是需要依赖：
sanic==19.9.0
Pillow==7.0.0
马哥教育Python网络班企业教练思路：
import randomimport stringimport uuidimport base64import platformfrom PIL import Image, ImageDraw,ImageFontfrom io import BytesIOfrom sanic import Sanicfrom sanic.response import HTTPResponse,textfrom sanic.views import HTTPMethodView
app = Sanic()
session = {}
class VerifyCode:    def __init__(self, numbers:int):        """        指定:生成的数量        """        self.number = numbers
    def draw_lines(self, draw, num, width, height):        """划线"""
        x1 = random.randint(0, width / 2)        y1 = random.randint(0, height / 2)        x2 = random.randint(0, width)        y2 = random.randint(height / 2, height)        draw.line(((x1, y1), (x2, y2)), fill='black', width=1)
    def random_color(self):        """随机颜色"""        return (random.randint(32, 127), random.randint(32, 127), random.randint(32, 127))    def gene_text(self):        """生成验证码"""        return "".join(random.sample(string.ascii_letters+string.digits, self.number))
    def get_verify_code(self):        """        draw.text()：            文字的绘制，第一个参数指定绘制的起始点（文本的左上角所在位置），第二个参数指定文本内容，第三个参数指定文本的颜色，第四个参数指定字体（通过ImageFont类来定义）        """        code = self.gene_text()        width, height = 130, 30        im = Image.new("RGB


    
", (width, height), "white")                sysstr = platform.system()        font = None        if sysstr == "Windows":            font = ImageFont.truetype("C:\WINDOWS\Fonts\STXINGKA.TTF", 25)        elif sysstr == "Darwin":            font = ImageFont.truetype('/Library/Fonts/AppleMyungjo.ttf', 25)        draw = ImageDraw.Draw(im)        for item in range(self.number):            draw.text((5+random.randint(-5,5)+23*item, 5+random.randint(-5, 5)), text=code[item],                      fill=self.random_color(), font=font)            self.draw_lines(draw, self.number, width, height)        return im, code

class SimpleView(HTTPMethodView):    body = """        <html>            <head>                <meta charset="UTF-8">                    <title>登录title>                    <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap@3.3.7/dist/css/bootstrap.min.css" integrity="sha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va+PmSTsz/K68vbdEjh4u" crossorigin="anonymous">                                        <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap@3.3.7/dist/css/bootstrap-theme.min.css" integrity="sha384-rHyoN1iRsVXV4nD0JutlnGaslCJuC7uwjduW9SVrLvRYooPp2bWYgmgJQIXwl/Sp" crossorigin="anonymous">                                        <script src="https://cdn.jsdelivr.net/npm/bootstrap@3.3.7/dist/js/bootstrap.min.js" integrity="sha384-Tc5IQib027qvyjSMfHjOMaLkfuWVxZxUPnCJA7l2mCWNIpG9mGCD8wGNIcPD7Txa" crossorigin="anonymous">script>            head>            <body>                <form class="form-inline" method="post" action="/code">                    <div>                        <div class="form-group">{error}