title: Flask self.errors.append() - AttributeError: 'tuple' object has no attribute 'append'
body: <p>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. </p>
  
  <p>here is my files: <br/>
  <strong>forms:</strong></p>
  
  <pre><code>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
  </code></pre>
  
  <p><strong>views:</strong></p>
  
  <pre><code>#!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)
  </code></pre>
  
  <p>The error is:</p>
  
  <pre><code>Traceback (most recent call last) File &lt;br&gt; "/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'
  </code></pre>