unit two verify | Python Fiddle

import cgi
import webapp2
import re

form2 = """
<!DOCTYPE html>

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

</head>

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

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

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

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

</html>
"""
def escape_html(s):
    return cgi.escape(s, quote = True)

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

def valid_username(username):
    return USER_RE.match(username)
def valid_password(password1, password2):
    return PASS_RE.match(password1)
def valid_verify(password1, password2):
    if password1 == password2 and PASS_RE.match(password2):
        return True
    return False
def valid_email(email):
    if EMAIL_RE.match(email) or email == "":
        return True
    return False

class VerifyHandler(webapp2.RequestHandler):
    def writeform(self, uname="", user_error="", password_error="", verify_error="", user_email="", email_error=""):
        self.response.out.write(form2 % {'uname': uname, 'user_error': user_error, 'password_error': password_error, 'verify_error': verify_error, 'user_email': user_email, 'email_error': email_error})
    
    def get(self):
        self.writeform()

def post(self):
        user_report=""
        password_report=""
        verify_report=""
        email_report=""
        username = self.request.get('username')
        password = self.request.get('password')
        verify = self.request.get('verify')
        email = self.request.get('email')

if valid_username(username) and valid_password(password, verify) and valid_verify(password, verify) and valid_email(email):
            self.redirect('/unit2/accepted?username=' + username)
        else:
            if not valid_username(username):
                user_report="That is not a valid username"
            if not valid_password(password, verify):
                password_report="That is not a valid password"
            else:
                if not valid_verify(password, verify):
                    verify_report="Your passwords didn't match"
            if not valid_email(email):
                email_report="That's not a valid email"
            self.writeform(username,user_report, password_report, verify_report, email, email_report)

class AcceptedHandler(webapp2.RequestHandler):
    #username = os.environment('QUERY_STRING')
    def get(self):
        username = self.request.get('username')
        self.response.out.write('Welcome, ' + username)
            
app = webapp2.WSGIApplication([('/unit2/verify', VerifyHandler),
                               ('/unit2/accepted', AcceptedHandler)],
                              debug=True)

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