Untitled

import cgi
import re
import webapp2

form="""
<!DOCTYPE html>

<html>
 <head>
   <title>Sign Up</title>
   <style type="text/css">
     .label {text-align: right}
     .error {color: red}
   </style>

 </head>

 <body>
   <center> <br><br><br><br>
   <h2>Signup</h2>
   <form method="post">
     <table>
       <tr>
         <td class="label">
           Username
         </td>
         <td>
           <input type="text" name="username" value="%(username)s">
         </td>
         <td class="error">%(user_error)s</td>
       </tr>

       <tr>
         <td class="label">
           Password
         </td>
         <td>
           <input type="password" name="password" value="%(password)s">
         </td>
         <td class="error">%(pass_error)s</td>
       </tr>

       <tr>
         <td class="label">
           Verify Password
         </td>
         <td>
           <input type="password" name="verify" value="%(verify)s">
         </td>
         <td class="error">%(verify_error)s</td>
       </tr>

       <tr>
         <td class="label">
           Email (optional)
         </td>
         <td>
           <input type="text" name="email" value="%(email)s">
         </td>
         <td class="error">%(email_error)s</td>
       </tr>
     </table>

     <input type="submit">
   </form>
   </center>
 </body>

</html>

"""

user_re = re.compile(r"^[a-zA-Z0-9_-]{3,20}$")
pass_re = re.compile(r"^.{3,20}$")
email_re = re.compile(r"^[\S]+@[\S]+\.[\S]+$")

def escape_html(s):
    return cgi.escape(s, quote = True)

def check_username(username):
    return username and user_re.match(username)

def check_password(password):
    return password and pass_re.match(password)

def check_email(email):
    return not email or email_re.match(email)


class NewPage(webapp2.RequestHandler):

    def write(self, *a, **kw):
        self.response.out.write(*a, **kw)

    def get(self):
        params = dict(username="", password="", verify="", email="",user_error="", pass_error="", verify_error="", email_error="")
        self.response.out.write(form % params)

    def post(self):
        have_error = False
        username = self.request.get('username')
        password = self.request.get('password')
        verify = self.request.get('verify')
        email = self.request.get('email')

        params = dict(username=username, password="", verify="", email=email, user_error="", pass_error="", verify_error="", email_error="")

        if not check_username(username):
            params['user_error'] = "That's not a valid username."
            have_error = True
        if not check_password(password):
            params['pass_error'] = "That wasn't a valid password."
            have_error = True
        elif password != verify:
            params['verify_error'] = "Your passwords didn't match."
            have_error = True
        if not check_email(email):
            params['email_error'] = "That's not a valid email."
            have_error = True
        if have_error:
            self.response.out.write(form % params)
        else:
            self.redirect('/welcome?username=' + username)


class Welcome(webapp2.RequestHandler):
    def get(self):
        username = self.request.get('username')
        if check_username(username):
            self.response.out.write("Welcome {{%s}}!" % username)
        else:
            self.redirect('/')

app = webapp2.WSGIApplication([('/', NewPage),
                                ('/welcome', Welcome)],
                                debug=True)