Flask self.errors.append() - AttributeError: 'tuple' object has no attribute 'append'

Question

My small registration app gives and error when I try to validate the submited data by user and check if the entered e-mail exists.

here is my files:
forms:

from flask.ext.wtf import Form
from wtforms import TextField, BooleanField, PasswordField, TextAreaField, validators
from wtforms.validators import Required
from app import models

class RegisterForm(Form):
"""RegisterForm class needed for retrieving data from user"""
username = TextField('username', [validators.Length(min=3, max=50), validators.Required()])
email = TextField('email', [validators.Length(min=3, max=100), validators.Required()])
password = PasswordField('password', [validators.Required()])
age = TextField('age', [validators.Length(min=1, max=3), validators.Required()])
about_user = TextAreaField('about_user', [validators.Length(max=500)])
img_url = TextField('img_url')


def email_unique(self, email):
    if models.User.query.filter_by(email = email).first() != None:
        self.email.errors.append('This E-mail address is already in use. Please choose another one.') 
        return False

views:

#!flask/bin/python
from app import app, db, lm
from flask import render_template, url_for, flash, g, redirect, session, request
from flask.ext.login import login_user, logout_user, current_user, login_required
from forms import LoginForm, RegisterForm, EditForm
from models import User

@app.route('/register', methods = ['GET', 'POST'])
def register():
    form = RegisterForm()
    #makes the username unique
    u_unique =  form.username.data
    u_unique = User.unique_username(u_unique)

    #validates email adress and checks if it already exists or not 
    form.email_unique(form.email.data)

    if form.validate_on_submit():
        user = User(
            u_unique,
            form.password.data, 
            form.email.data, 
            form.age.data, 
            form.about_user.data,
            form.img_url.data)
        db.session.add(user)
        db.session.commit()
        flash('Thank you for your registration')
        flash('Your username is: ' + str(u_unique))
        return redirect(url_for('login'))
    else:
        for error in form.errors:
            flash(error)

    return render_template('register.html',
        title = 'Registeration',
        form = form)

The error is:

Traceback (most recent call last) File <br> "/home/maksad/Desktop/faskMonkey/flask/lib/python2.7/site-packages/flask/app.py", line 1701, in __call__ return self.wsgi_app(environ, start_response) 
File "/home/maksad/Desktop/faskMonkey/flask/lib/python2.7/site-packages/flask/app.py", line 1689, in wsgi_app response = self.make_response(self.handle_exception(e)) 
File "/home/maksad/Desktop/faskMonkey/flask/lib/python2.7/site-packages/flask/app.py", line 1687, in wsgi_app response = self.full_dispatch_request() 
File "/home/maksad/Desktop/faskMonkey/flask/lib/python2.7/site-packages/flask/app.py", line 1360, in full_dispatch_request rv = self.handle_user_exception(e) 
File "/home/maksad/Desktop/faskMonkey/flask/lib/python2.7/site-packages/flask/app.py", line 1358, in full_dispatch_request rv = self.dispatch_request() 
File "/home/maksad/Desktop/faskMonkey/flask/lib/python2.7/site-packages/flask/app.py", line 1344, in dispatch_request return self.view_functions[rule.endpoint](**req.view_args) 
File "/home/maksad/Desktop/faskMonkey/app/views.py", line 92, in register form.email_unique(form.email.data) 
File "/home/maksad/Desktop/faskMonkey/app/forms.py", line 26, in email_unique
 self.email.errors.append('This E-mail address is already in use. Please choose another one.')
 AttributeError: 'tuple' object has no attribute 'append'

Answer 1

The tuple objects cannot append. Instead, convert to a list using list(), and append, and then convert back, as such:

>>> obj1 = (6, 1, 2, 6, 3)
>>> obj2 = list(obj1) #Convert to list
>>> obj2.append(8)
>>> print obj2
[6, 1, 2, 6, 3, 8]
>>> obj1 = tuple(obj2) #Convert back to tuple
>>> print obj1
(6, 1, 2, 6, 3, 8)

Hope this helps!