easy_install WTForms
# or
pip install WTForms

from wtforms import Form, BooleanField, StringField, validators

class RegistrationForm(Form):
 username  = StringField('Username', [validators.Length(min=4, max=25)])
 email  = StringField('Email Address', [validators.Length(min=6, max=35)])
 accept_rules = BooleanField('I accept the site rules', [validators.InputRequired()])

class ProfileForm(Form):
 birthday = DateTimeField('Your Birthday', format='%m/%d/%y')
 signature = TextAreaField('Forum Signature')

class AdminProfileForm(ProfileForm):
 username = StringField('Username', [validators.Length(max=40)])
 level = IntegerField('User Level', [validators.NumberRange(min=0, max=10)])

def register(request):
 form = RegistrationForm(request.POST)
 if request.method == 'POST' and form.validate():
  user = User()
  user.username = form.username.data
  user.email = form.email.data
  user.save()
  redirect('register')
 return render_response('register.html', form=form)

def edit_profile(request):
 user = request.current_user
 form = ProfileForm(request.POST, user)
 if request.method == 'POST' and form.validate():
  form.populate_obj(user)
  user.save()
  redirect('edit_profile')
 return render_response('edit_profile.html', form=form)

>>> from wtforms import Form, StringField, validators
>>> class UsernameForm(Form):
...  username = StringField('Username', [validators.Length(min=5)], default=u'test')
...
>>> form = UsernameForm()
>>> form['username']
<wtforms.fields.StringField object at 0x827eccc>
>>> form.username.data
u'test'
>>> form.validate()
False
>>> form.errors
{'username': [u'Field must be at least 5 characters long.']}

>>> form2 = UsernameForm(username=u'Robert')
>>> form2.data
{'username': u'Robert'}
>>> form2.validate()
True

def change_username(request):
 user = request.current_user
 form = ChangeUsernameForm(request.POST, user, username='silly')
 if request.method == 'POST' and form.validate():
  user.username = form.username.data
  user.save()
  return redirect('change_username')
 return render_response('change_username.html', form=form)

class ChangeEmailForm(Form):
 email = StringField('Email', [validators.Length(min=6, max=120), validators.Email()])

class ChangeEmailForm(Form):
 email = StringField('Email', [
  validators.Length(min=6, message=_(u'Little short for an email address?')),
  validators.Email(message=_(u'That\'s not a valid email address.'))
 ])

>>> from wtforms import Form, StringField
>>> class SimpleForm(Form):
... content = StringField('content')
...
>>> form = SimpleForm(content='foobar')
>>> str(form.content)
'<input id="content" name="content" type="text" value="foobar" />'
>>> unicode(form.content)
u'<input id="content" name="content" type="text" value="foobar" />'

>>> form.content(style="width: 200px;", class_="bar")
u'<input class="bar" id="content" name="content" style="width: 200px;" type="text" value="foobar" />'

class LoginForm(Form):
 username = StringField('Username')
 password = PasswordField('Password')

form = LoginForm()

<form method="POST" action="/login">
 <div>{{ form.username.label }}: {{ form.username(class="css_class") }}</div>
 <div>{{ form.password.label }}: {{ form.password() }}</div>
</form>

{% load wtforms %}
<form method="POST" action="/login">
 <div>
  {{ form.username.label }}:
  {% form_field form.username class="css_class" %}
 </div>
 <div>
  {{ form.password.label }}:
  {{ form.password }}
 </div>
</form>

<form method="POST" action="/login">
 <div>
  <label for="username">Username</label>:
  <input class="css_class" id="username" name="username" type="text" value="" />
 </div>
 <div>
  <label for="password">Password</label>:
  <input id="password" name="password" type="password" value="" />
 </div>
</form>

<form method="POST" action="/login">
 <div>{{ form.username.label }}: {{ form.username(class="css_class") }}</div>
 {% if form.username.errors %}
  <ul class="errors">{% for error in form.username.errors %}<li>{{ error }}</li>{% endfor %}</ul>
 {% endif %}

 <div>{{ form.password.label }}: {{ form.password() }}</div>
 {% if form.password.errors %}
  <ul class="errors">{% for error in form.password.errors %}<li>{{ error }}</li>{% endfor %}</ul>
 {% endif %}
</form>

{% if form.errors %}
 <ul class="errors">
  {% for field_name, field_errors in form.errors|dictsort if field_errors %}
   {% for error in field_errors %}
    <li>{{ form[field_name].label }}: {{ error }}</li>
   {% endfor %}
  {% endfor %}
 </ul>
{% endif %}

from wtforms.validators import ValidationError

def is_42(form, field):
 if field.data != 42:
  raise ValidationError('Must be 42')

class FourtyTwoForm(Form):
 num = IntegerField('Number', [is_42])

class FourtyTwoForm(Form):
 num = IntegerField('Number')

 def validate_num(form, field):
  if field.data != 42:
   raise ValidationError(u'Must be 42')

class TagListField(Field):
 widget = TextInput()

 def _value(self):
  if self.data:
   return u', '.join(self.data)
  else:
   return u''

 def process_formdata(self, valuelist):
  if valuelist:
   self.data = [x.strip() for x in valuelist[0].split(',')]
  else:
   self.data = []

class TagListField(Field):
 widget = TextInput()

 def __init__(self, label=None, validators=None,
     **kwargs):
  super(TagListField, self).__init__(label, validators, **kwargs)

 def _value(self):
  if self.data:
   r = u''
   for obj in self.data:
    r += self.obj_to_str(obj)
   return u''
  else:
   return u''

 def process_formdata(self, valuelist):
  print 'process_formdata..'
  print valuelist
  if valuelist:
   tags = self._remove_duplicates([x.strip() for x in valuelist[0].split(',')])
   self.data = [self.str_to_obj(tag) for tag in tags]
  else:
   self.data = None

 def pre_validate(self, form):
  pass

 @classmethod
 def _remove_duplicates(cls, seq):
  """去重"""
  d = {}
  for item in seq:
   if item.lower() not in d:
    d[item.lower()] = True
    yield item

 @classmethod
 def str_to_obj(cls, tag):
  """将字符串转换位obj对象"""
  tag_obj = Tag.query.filter_by(name=tag).first()
  if tag_obj is None:
   tag_obj = Tag(name=tag)
  return tag_obj

 @classmethod
 def obj_to_str(cls, obj):
  """将对象转换为字符串"""
  if obj:
   return obj.name
  else:
   return u''

class TagListField(Field):
 widget = TextInput()
 
 def __init__(self, label=None, validators=None,
     **kwargs):
  super(TagListField, self).__init__(label, validators, **kwargs)
 
 def _value(self):
  if self.data:
   r = u''
   for obj in self.data:
    r += self.obj_to_str(obj)
   return u''
  else:
   return u''
 
 def process_formdata(self, valuelist):
  print 'process_formdata..'
  print valuelist
  if valuelist:
   tags = self._remove_duplicates([x.strip() for x in valuelist[0].split(',')])
   self.data = [self.str_to_obj(tag) for tag in tags]
  else:
   self.data = None
 
 def pre_validate(self, form):
  pass
 
 @classmethod
 def _remove_duplicates(cls, seq):
  """去重"""
  d = {}
  for item in seq:
   if item.lower() not in d:
    d[item.lower()] = True
    yield item
 
 @classmethod
 def str_to_obj(cls, tag):
  """将字符串转换位obj对象"""
  tag_obj = Tag.query.filter_by(name=tag).first()
  if tag_obj is None:
   tag_obj = Tag(name=tag)
  return tag_obj
 
 @classmethod
 def obj_to_str(cls, obj):
  """将对象转换为字符串"""
  if obj:
   return obj.name
  else:
   return u''

...
class ArticleForm(Form):
 """编辑文章表单"""

 title = StringField(u'标题', validators=[Required()])
 category = QuerySelectField(u'分类', query_factory=get_category_factory(['id', 'name']), get_label='name')
 tags = TagListField(u'标签', validators=[Required()])
 content = PageDownField(u'正文', validators=[Required()])
 submit = SubmitField(u'发布')
...

...
class ArticleForm(Form):
 """编辑文章表单"""
 
 title = StringField(u'标题', validators=[Required()])
 category = QuerySelectField(u'分类', query_factory=get_category_factory(['id', 'name']), get_label='name')
 tags = TagListField(u'标签', validators=[Required()])
 content = PageDownField(u'正文', validators=[Required()])
 submit = SubmitField(u'发布')
...
在views.py中处理表单就很方便了：


def edit_article():
 """编辑文章"""

 form = ArticleForm()
 if form.validate_on_submit():
  article = Article(title=form.title.data, content=form.content.data)
  article.tags = form.tags.data
  article.category = form.category.data
  try:
   db.session.add(article)
   db.session.commit()
  except:
   db.session.rollback()
 return render_template('dashboard/edit.html', form=form)

def edit_article():
 """编辑文章"""
 
 form = ArticleForm()
 if form.validate_on_submit():
  article = Article(title=form.title.data, content=form.content.data)
  article.tags = form.tags.data
  article.category = form.category.data
  try:
   db.session.add(article)
   db.session.commit()
  except:
   db.session.rollback()
 return render_template('dashboard/edit.html', form=form)