a simple example to realize "rot13" encode

rot13cipher.py

import webapp2
import cgi
import codecs

# build a simple html form
form = """
<form method="post">
<h1 style="color: green">Let's use rot13 cipher!</h1>
<textarea name="text" rows="8" cols="40">%(text)s</textarea>
<input type="submit">
</form>
"""

# build a function that make the special characters into character entities, such like "&" -- "&amp;"
def escape_html(s):
    return cgi.escape(s, quote = True)

class MainPage(webapp2.RequestHandler):
    def write_form(self, text=""):
        self.response.out.write(form % {'text': escape_html(text)})

    def get(self):
        self.write_form()

    def post(self):
        user_text = self.request.get('text')

        # 'ignore' is to ignore Chinese characters
        translated_text = codecs.encode(user_text, 'rot_13', 'ignore')

        self.write_form(translated_text)

app = webapp2.WSGIApplication([
    ('/', MainPage),
], debug=True)