"""
36. Generating HTML forms from models

Django provides shortcuts for creating Form objects from a model class and a
model instance.

The function django.newforms.form_for_model() takes a model class and returns
a Form that is tied to the model. This Form works just like any other Form,
with one additional method: save(). The save() method creates an instance
of the model and returns that newly created instance. It saves the instance to
the database if save(commit=True), which is default. If you pass
commit=False, then you'll get the object without committing the changes to the
database.

The function django.newforms.form_for_instance() takes a model instance and
returns a Form that is tied to the instance. This form works just like any
other Form, with one additional method: save(). The save()
method updates the model instance. It also takes a commit=True parameter.

The function django.newforms.save_instance() takes a bound form instance and a
model instance and saves the form's cleaned_data into the instance. It also takes
a commit=True parameter.
"""

from django.db import models

ARTICLE_STATUS = (
    (1, 'Draft'),
    (2, 'Pending'),
    (3, 'Live'),
)

STEERING_TYPE = (
    ('left', 'Left steering wheel'),
    ('right', 'Right steering wheel'),
)

FUEL_TYPE = (
    ('gas', 'Gasoline'),
    ('diesel', 'Diesel'),
    ('other', 'Other'),
)

TRANSMISSION_TYPE = (
    ('at', 'Automatic'),
    ('mt', 'Manual'),
    ('cvt', 'CVT'),
)

class Category(models.Model):
    name = models.CharField(max_length=20)
    slug = models.SlugField(max_length=20)
    url = models.CharField('The URL', max_length=40)

    def __unicode__(self):
        return self.name

class Writer(models.Model):
    name = models.CharField(max_length=50, help_text='Use both first and last names.')

    def __unicode__(self):
        return self.name

class Article(models.Model):
    headline = models.CharField(max_length=50)
    slug = models.SlugField()
    pub_date = models.DateField()
    created = models.DateField(editable=False)
    writer = models.ForeignKey(Writer)
    article = models.TextField()
    categories = models.ManyToManyField(Category, blank=True)
    status = models.IntegerField(choices=ARTICLE_STATUS, blank=True, null=True)

    def save(self):
        import datetime
        if not self.id:
            self.created = datetime.date.today()
        return super(Article, self).save()

    def __unicode__(self):
        return self.headline

class PhoneNumber(models.Model):
    phone = models.PhoneNumberField()
    description = models.CharField(max_length=20)

    def __unicode__(self):
        return self.phone

class Car(models.Model):
    name = models.CharField(max_length=50)
    steering = models.CharField(max_length=5, choices=STEERING_TYPE, default='left')
    fuel = models.CharField(max_length=10, choices=FUEL_TYPE)
    transmission = models.CharField(max_length=3, choices=TRANSMISSION_TYPE, blank=True, help_text='Leave empty if not applicable.')

__test__ = {'API_TESTS': """
>>> from django.newforms import form_for_model, form_for_instance, save_instance, BaseForm, Form, CharField
>>> import datetime

>>> Category.objects.all()
[]

>>> CategoryForm = form_for_model(Category)
>>> f = CategoryForm()
>>> print f
<tr><th><label for="id_name">Name:</label></th><td><input id="id_name" type="text" name="name" maxlength="20" /></td></tr>
<tr><th><label for="id_slug">Slug:</label></th><td><input id="id_slug" type="text" name="slug" maxlength="20" /></td></tr>
<tr><th><label for="id_url">The URL:</label></th><td><input id="id_url" type="text" name="url" maxlength="40" /></td></tr>
>>> print f.as_ul()
<li><label for="id_name">Name:</label> <input id="id_name" type="text" name="name" maxlength="20" /></li>
<li><label for="id_slug">Slug:</label> <input id="id_slug" type="text" name="slug" maxlength="20" /></li>
<li><label for="id_url">The URL:</label> <input id="id_url" type="text" name="url" maxlength="40" /></li>
>>> print f['name']
<input id="id_name" type="text" name="name" maxlength="20" />

>>> f = CategoryForm(auto_id=False)
>>> print f.as_ul()
<li>Name: <input type="text" name="name" maxlength="20" /></li>
<li>Slug: <input type="text" name="slug" maxlength="20" /></li>
<li>The URL: <input type="text" name="url" maxlength="40" /></li>

>>> f = CategoryForm({'name': 'Entertainment', 'slug': 'entertainment', 'url': 'entertainment'})
>>> f.is_valid()
True
>>> f.cleaned_data
{'url': u'entertainment', 'name': u'Entertainment', 'slug': u'entertainment'}
>>> obj = f.save()
>>> obj
<Category: Entertainment>
>>> Category.objects.all()
[<Category: Entertainment>]

>>> f = CategoryForm({'name': "It's a test", 'slug': 'its-test', 'url': 'test'})
>>> f.is_valid()
True
>>> f.cleaned_data
{'url': u'test', 'name': u"It's a test", 'slug': u'its-test'}
>>> obj = f.save()
>>> obj
<Category: It's a test>
>>> Category.objects.order_by('name')
[<Category: Entertainment>, <Category: It's a test>]

If you call save() with commit=False, then it will return an object that
hasn't yet been saved to the database. In this case, it's up to you to call
save() on the resulting model instance.
>>> f = CategoryForm({'name': 'Third test', 'slug': 'third-test', 'url': 'third'})
>>> f.is_valid()
True
>>> f.cleaned_data
{'url': u'third', 'name': u'Third test', 'slug': u'third-test'}
>>> obj = f.save(commit=False)
>>> obj
<Category: Third test>
>>> Category.objects.order_by('name')
[<Category: Entertainment>, <Category: It's a test>]
>>> obj.save()
>>> Category.objects.order_by('name')
[<Category: Entertainment>, <Category: It's a test>, <Category: Third test>]

If you call save() with invalid data, you'll get a ValueError.
>>> f = CategoryForm({'name': '', 'slug': '', 'url': 'foo'})
>>> f.errors
{'name': [u'This field is required.'], 'slug': [u'This field is required.']}
>>> f.cleaned_data
Traceback (most recent call last):
...
AttributeError: 'CategoryForm' object has no attribute 'cleaned_data'
>>> f.save()
Traceback (most recent call last):
...
ValueError: The Category could not be created because the data didn't validate.
>>> f = CategoryForm({'name': '', 'slug': '', 'url': 'foo'})
>>> f.save()
Traceback (most recent call last):
...
ValueError: The Category could not be created because the data didn't validate.

Create a couple of Writers.
>>> w = Writer(name='Mike Royko')
>>> w.save()
>>> w = Writer(name='Bob Woodward')
>>> w.save()

ManyToManyFields are represented by a MultipleChoiceField, ForeignKeys and any
fields with the 'choices' attribute are represented by a ChoiceField.
>>> ArticleForm = form_for_model(Article)
>>> f = ArticleForm(auto_id=False)
>>> print f
<tr><th>Headline:</th><td><input type="text" name="headline" maxlength="50" /></td></tr>
<tr><th>Slug:</th><td><input type="text" name="slug" maxlength="50" /></td></tr>
<tr><th>Pub date:</th><td><input type="text" name="pub_date" /></td></tr>
<tr><th>Writer:</th><td><select name="writer">
<option value="" selected="selected">---------</option>
<option value="1">Mike Royko</option>
<option value="2">Bob Woodward</option>
</select></td></tr>
<tr><th>Article:</th><td><textarea rows="10" cols="40" name="article"></textarea></td></tr>
<tr><th>Status:</th><td><select name="status">
<option value="" selected="selected">---------</option>
<option value="1">Draft</option>
<option value="2">Pending</option>
<option value="3">Live</option>
</select></td></tr>
<tr><th>Categories:</th><td><select multiple="multiple" name="categories">
<option value="1">Entertainment</option>
<option value="2">It&#39;s a test</option>
<option value="3">Third test</option>
</select><br /> Hold down "Control", or "Command" on a Mac, to select more than one.</td></tr>

You can restrict a form to a subset of the complete list of fields
by providing a 'fields' argument. If you try to save a
model created with such a form, you need to ensure that the fields
that are _not_ on the form have default values, or are allowed to have
a value of None. If a field isn't specified on a form, the object created
from the form can't provide a value for that field!
>>> PartialArticleForm = form_for_model(Article, fields=('headline','pub_date'))
>>> f = PartialArticleForm(auto_id=False)
>>> print f
<tr><th>Headline:</th><td><input type="text" name="headline" maxlength="50" /></td></tr>
<tr><th>Pub date:</th><td><input type="text" name="pub_date" /></td></tr>

You can pass a custom Form class to form_for_model. Make sure it's a
subclass of BaseForm, not Form.
>>> class CustomForm(BaseForm):
...     def say_hello(self):
...         print 'hello'
>>> CategoryForm = form_for_model(Category, form=CustomForm)
>>> f = CategoryForm()
>>> f.say_hello()
hello

Use form_for_instance to create a Form from a model instance. The difference
between this Form and one created via form_for_model is that the object's
current values are inserted as 'initial' data in each Field.
>>> w = Writer.objects.get(name='Mike Royko')
>>> RoykoForm = form_for_instance(w)
>>> f = RoykoForm(auto_id=False)
>>> print f
<tr><th>Name:</th><td><input type="text" name="name" value="Mike Royko" maxlength="50" /><br />Use both first and last names.</td></tr>

>>> art = Article(headline='Test article', slug='test-article', pub_date=datetime.date(1988, 1, 4), writer=w, article='Hello.')
>>> art.save()
>>> art.id
1
>>> TestArticleForm = form_for_instance(art)
>>> f = TestArticleForm(auto_id=False)
>>> print f.as_ul()
<li>Headline: <input type="text" name="headline" value="Test article" maxlength="50" /></li>
<li>Slug: <input type="text" name="slug" value="test-article" maxlength="50" /></li>
<li>Pub date: <input type="text" name="pub_date" value="1988-01-04" /></li>
<li>Writer: <select name="writer">
<option value="">---------</option>
<option value="1" selected="selected">Mike Royko</option>
<option value="2">Bob Woodward</option>
</select></li>
<li>Article: <textarea rows="10" cols="40" name="article">Hello.</textarea></li>
<li>Status: <select name="status">
<option value="" selected="selected">---------</option>
<option value="1">Draft</option>
<option value="2">Pending</option>
<option value="3">Live</option>
</select></li>
<li>Categories: <select multiple="multiple" name="categories">
<option value="1">Entertainment</option>
<option value="2">It&#39;s a test</option>
<option value="3">Third test</option>
</select>  Hold down "Control", or "Command" on a Mac, to select more than one.</li>
>>> f = TestArticleForm({'headline': u'Test headline', 'slug': 'test-headline', 'pub_date': u'1984-02-06', 'writer': u'1', 'article': 'Hello.'})
>>> f.is_valid()
True
>>> test_art = f.save()
>>> test_art.id
1
>>> test_art = Article.objects.get(id=1)
>>> test_art.headline
u'Test headline'

You can create a form over a subset of the available fields
by specifying a 'fields' argument to form_for_instance.
>>> PartialArticleForm = form_for_instance(art, fields=('headline', 'slug', 'pub_date'))
>>> f = PartialArticleForm({'headline': u'New headline', 'slug': 'new-headline', 'pub_date': u'1988-01-04'}, auto_id=False)
>>> print f.as_ul()
<li>Headline: <input type="text" name="headline" value="New headline" maxlength="50" /></li>
<li>Slug: <input type="text" name="slug" value="new-headline" maxlength="50" /></li>
<li>Pub date: <input type="text" name="pub_date" value="1988-01-04" /></li>
>>> f.is_valid()
True
>>> new_art = f.save()
>>> new_art.id
1
>>> new_art = Article.objects.get(id=1)
>>> new_art.headline
u'New headline'

Add some categories and test the many-to-many form output.
>>> new_art.categories.all()
[]
>>> new_art.categories.add(Category.objects.get(name='Entertainment'))
>>> new_art.categories.all()
[<Category: Entertainment>]
>>> TestArticleForm = form_for_instance(new_art)
>>> f = TestArticleForm(auto_id=False)
>>> print f.as_ul()
<li>Headline: <input type="text" name="headline" value="New headline" maxlength="50" /></li>
<li>Slug: <input type="text" name="slug" value="new-headline" maxlength="50" /></li>
<li>Pub date: <input type="text" name="pub_date" value="1988-01-04" /></li>
<li>Writer: <select name="writer">
<option value="">---------</option>
<option value="1" selected="selected">Mike Royko</option>
<option value="2">Bob Woodward</option>
</select></li>
<li>Article: <textarea rows="10" cols="40" name="article">Hello.</textarea></li>
<li>Status: <select name="status">
<option value="" selected="selected">---------</option>
<option value="1">Draft</option>
<option value="2">Pending</option>
<option value="3">Live</option>
</select></li>
<li>Categories: <select multiple="multiple" name="categories">
<option value="1" selected="selected">Entertainment</option>
<option value="2">It&#39;s a test</option>
<option value="3">Third test</option>
</select>  Hold down "Control", or "Command" on a Mac, to select more than one.</li>

>>> f = TestArticleForm({'headline': u'New headline', 'slug': u'new-headline', 'pub_date': u'1988-01-04',
...     'writer': u'1', 'article': u'Hello.', 'categories': [u'1', u'2']})
>>> new_art = f.save()
>>> new_art.id
1
>>> new_art = Article.objects.get(id=1)
>>> new_art.categories.order_by('name')
[<Category: Entertainment>, <Category: It's a test>]

Now, submit form data with no categories. This deletes the existing categories.
>>> f = TestArticleForm({'headline': u'New headline', 'slug': u'new-headline', 'pub_date': u'1988-01-04',
...     'writer': u'1', 'article': u'Hello.'})
>>> new_art = f.save()
>>> new_art.id
1
>>> new_art = Article.objects.get(id=1)
>>> new_art.categories.all()
[]

Create a new article, with categories, via the form.
>>> ArticleForm = form_for_model(Article)
>>> f = ArticleForm({'headline': u'The walrus was Paul', 'slug': u'walrus-was-paul', 'pub_date': u'1967-11-01',
...     'writer': u'1', 'article': u'Test.', 'categories': [u'1', u'2']})
>>> new_art = f.save()
>>> new_art.id
2
>>> new_art = Article.objects.get(id=2)
>>> new_art.categories.order_by('name')
[<Category: Entertainment>, <Category: It's a test>]

Create a new article, with no categories, via the form.
>>> ArticleForm = form_for_model(Article)
>>> f = ArticleForm({'headline': u'The walrus was Paul', 'slug': u'walrus-was-paul', 'pub_date': u'1967-11-01',
...     'writer': u'1', 'article': u'Test.'})
>>> new_art = f.save()
>>> new_art.id
3
>>> new_art = Article.objects.get(id=3)
>>> new_art.categories.all()
[]

Create a new article, with categories, via the form, but use commit=False.
The m2m data won't be saved until save_m2m() is invoked on the form.
>>> ArticleForm = form_for_model(Article)
>>> f = ArticleForm({'headline': u'The walrus was Paul', 'slug': 'walrus-was-paul', 'pub_date': u'1967-11-01',
...     'writer': u'1', 'article': u'Test.', 'categories': [u'1', u'2']})
>>> new_art = f.save(commit=False)

# Manually save the instance
>>> new_art.save()
>>> new_art.id
4

# The instance doesn't have m2m data yet
>>> new_art = Article.objects.get(id=4)
>>> new_art.categories.all()
[]

# Save the m2m data on the form
>>> f.save_m2m()
>>> new_art.categories.order_by('name')
[<Category: Entertainment>, <Category: It's a test>]

Here, we define a custom Form. Because it happens to have the same fields as
the Category model, we can use save_instance() to apply its changes to an
existing Category instance.
>>> class ShortCategory(Form):
...     name = CharField(max_length=5)
...     slug = CharField(max_length=5)
...     url = CharField(max_length=3)
>>> cat = Category.objects.get(name='Third test')
>>> cat
<Category: Third test>
>>> cat.id
3
>>> sc = ShortCategory({'name': 'Third', 'slug': 'third', 'url': '3rd'})
>>> save_instance(sc, cat)
<Category: Third>
>>> Category.objects.get(id=3)
<Category: Third>

Here, we demonstrate that choices for a ForeignKey ChoiceField are determined
at runtime, based on the data in the database when the form is displayed, not
the data in the database when the form is instantiated.
>>> ArticleForm = form_for_model(Article)
>>> f = ArticleForm(auto_id=False)
>>> print f.as_ul()
<li>Headline: <input type="text" name="headline" maxlength="50" /></li>
<li>Slug: <input type="text" name="slug" maxlength="50" /></li>
<li>Pub date: <input type="text" name="pub_date" /></li>
<li>Writer: <select name="writer">
<option value="" selected="selected">---------</option>
<option value="1">Mike Royko</option>
<option value="2">Bob Woodward</option>
</select></li>
<li>Article: <textarea rows="10" cols="40" name="article"></textarea></li>
<li>Status: <select name="status">
<option value="" selected="selected">---------</option>
<option value="1">Draft</option>
<option value="2">Pending</option>
<option value="3">Live</option>
</select></li>
<li>Categories: <select multiple="multiple" name="categories">
<option value="1">Entertainment</option>
<option value="2">It&#39;s a test</option>
<option value="3">Third</option>
</select>  Hold down "Control", or "Command" on a Mac, to select more than one.</li>
>>> Category.objects.create(name='Fourth', url='4th')
<Category: Fourth>
>>> Writer.objects.create(name='Carl Bernstein')
<Writer: Carl Bernstein>
>>> print f.as_ul()
<li>Headline: <input type="text" name="headline" maxlength="50" /></li>
<li>Slug: <input type="text" name="slug" maxlength="50" /></li>
<li>Pub date: <input type="text" name="pub_date" /></li>
<li>Writer: <select name="writer">
<option value="" selected="selected">---------</option>
<option value="1">Mike Royko</option>
<option value="2">Bob Woodward</option>
<option value="3">Carl Bernstein</option>
</select></li>
<li>Article: <textarea rows="10" cols="40" name="article"></textarea></li>
<li>Status: <select name="status">
<option value="" selected="selected">---------</option>
<option value="1">Draft</option>
<option value="2">Pending</option>
<option value="3">Live</option>
</select></li>
<li>Categories: <select multiple="multiple" name="categories">
<option value="1">Entertainment</option>
<option value="2">It&#39;s a test</option>
<option value="3">Third</option>
<option value="4">Fourth</option>
</select>  Hold down "Control", or "Command" on a Mac, to select more than one.</li>

# ModelChoiceField ############################################################

>>> from django.newforms import ModelChoiceField, ModelMultipleChoiceField

>>> f = ModelChoiceField(Category.objects.all())
>>> list(f.choices)
[(u'', u'---------'), (1, u'Entertainment'), (2, u"It's a test"), (3, u'Third'), (4, u'Fourth')]
>>> f.clean('')
Traceback (most recent call last):
...
ValidationError: [u'This field is required.']
>>> f.clean(None)
Traceback (most recent call last):
...
ValidationError: [u'This field is required.']
>>> f.clean(0)
Traceback (most recent call last):
...
ValidationError: [u'Select a valid choice. That choice is not one of the available choices.']
>>> f.clean(3)
<Category: Third>
>>> f.clean(2)
<Category: It's a test>

# Add a Category object *after* the ModelChoiceField has already been
# instantiated. This proves clean() checks the database during clean() rather
# than caching it at time of instantiation.
>>> Category.objects.create(name='Fifth', url='5th')
<Category: Fifth>
>>> f.clean(5)
<Category: Fifth>

# Delete a Category object *after* the ModelChoiceField has already been
# instantiated. This proves clean() checks the database during clean() rather
# than caching it at time of instantiation.
>>> Category.objects.get(url='5th').delete()
>>> f.clean(5)
Traceback (most recent call last):
...
ValidationError: [u'Select a valid choice. That choice is not one of the available choices.']

>>> f = ModelChoiceField(Category.objects.filter(pk=1), required=False)
>>> print f.clean('')
None
>>> f.clean('')
>>> f.clean('1')
<Category: Entertainment>
>>> f.clean('100')
Traceback (most recent call last):
...
ValidationError: [u'Select a valid choice. That choice is not one of the available choices.']

# queryset can be changed after the field is created.
>>> f.queryset = Category.objects.exclude(name='Fourth')
>>> list(f.choices)
[(u'', u'---------'), (1, u'Entertainment'), (2, u"It's a test"), (3, u'Third')]
>>> f.clean(3)
<Category: Third>
>>> f.clean(4)
Traceback (most recent call last):
...
ValidationError: [u'Select a valid choice. That choice is not one of the available choices.']


# ModelMultipleChoiceField ####################################################

>>> f = ModelMultipleChoiceField(Category.objects.all())
>>> list(f.choices)
[(1, u'Entertainment'), (2, u"It's a test"), (3, u'Third'), (4, u'Fourth')]
>>> f.clean(None)
Traceback (most recent call last):
...
ValidationError: [u'This field is required.']
>>> f.clean([])
Traceback (most recent call last):
...
ValidationError: [u'This field is required.']
>>> f.clean([1])
[<Category: Entertainment>]
>>> f.clean([2])
[<Category: It's a test>]
>>> f.clean(['1'])
[<Category: Entertainment>]
>>> f.clean(['1', '2'])
[<Category: Entertainment>, <Category: It's a test>]
>>> f.clean([1, '2'])
[<Category: Entertainment>, <Category: It's a test>]
>>> f.clean((1, '2'))
[<Category: Entertainment>, <Category: It's a test>]
>>> f.clean(['100'])
Traceback (most recent call last):
...
ValidationError: [u'Select a valid choice. 100 is not one of the available choices.']
>>> f.clean('hello')
Traceback (most recent call last):
...
ValidationError: [u'Enter a list of values.']

# Add a Category object *after* the ModelMultipleChoiceField has already been
# instantiated. This proves clean() checks the database during clean() rather
# than caching it at time of instantiation.
>>> Category.objects.create(id=6, name='Sixth', url='6th')
<Category: Sixth>
>>> f.clean([6])
[<Category: Sixth>]

# Delete a Category object *after* the ModelMultipleChoiceField has already been
# instantiated. This proves clean() checks the database during clean() rather
# than caching it at time of instantiation.
>>> Category.objects.get(url='6th').delete()
>>> f.clean([6])
Traceback (most recent call last):
...
ValidationError: [u'Select a valid choice. 6 is not one of the available choices.']

>>> f = ModelMultipleChoiceField(Category.objects.all(), required=False)
>>> f.clean([])
[]
>>> f.clean(())
[]
>>> f.clean(['10'])
Traceback (most recent call last):
...
ValidationError: [u'Select a valid choice. 10 is not one of the available choices.']
>>> f.clean(['3', '10'])
Traceback (most recent call last):
...
ValidationError: [u'Select a valid choice. 10 is not one of the available choices.']
>>> f.clean(['1', '10'])
Traceback (most recent call last):
...
ValidationError: [u'Select a valid choice. 10 is not one of the available choices.']

# queryset can be changed after the field is created.
>>> f.queryset = Category.objects.exclude(name='Fourth')
>>> list(f.choices)
[(1, u'Entertainment'), (2, u"It's a test"), (3, u'Third')]
>>> f.clean([3])
[<Category: Third>]
>>> f.clean([4])
Traceback (most recent call last):
...
ValidationError: [u'Select a valid choice. 4 is not one of the available choices.']
>>> f.clean(['3', '4'])
Traceback (most recent call last):
...
ValidationError: [u'Select a valid choice. 4 is not one of the available choices.']


# PhoneNumberField ############################################################

>>> PhoneNumberForm = form_for_model(PhoneNumber)
>>> f = PhoneNumberForm({'phone': '(312) 555-1212', 'description': 'Assistance'})
>>> f.is_valid()
True
>>> f.cleaned_data
{'phone': u'312-555-1212', 'description': u'Assistance'}

# form_for_* blank choices ####################################################

Show the form for a new Car. Note that steering field doesn't include the blank choice,
because the field is obligatory and has an explicit default.
>>> CarForm = form_for_model(Car)
>>> f = CarForm(auto_id=False)
>>> print f
<tr><th>Name:</th><td><input type="text" name="name" maxlength="50" /></td></tr>
<tr><th>Steering:</th><td><select name="steering">
<option value="left" selected="selected">Left steering wheel</option>
<option value="right">Right steering wheel</option>
</select></td></tr>
<tr><th>Fuel:</th><td><select name="fuel">
<option value="" selected="selected">---------</option>
<option value="gas">Gasoline</option>
<option value="diesel">Diesel</option>
<option value="other">Other</option>
</select></td></tr>
<tr><th>Transmission:</th><td><select name="transmission">
<option value="" selected="selected">---------</option>
<option value="at">Automatic</option>
<option value="mt">Manual</option>
<option value="cvt">CVT</option>
</select><br />Leave empty if not applicable.</td></tr>

Create a Car, and display the form for modifying it. Note that now the fuel
selector doesn't include the blank choice as well, since the field is
obligatory and can not be changed to be blank.
>>> honda = Car(name='Honda Accord Wagon', steering='right', fuel='gas', transmission='at')
>>> honda.save()
>>> HondaForm = form_for_instance(honda)
>>> f = HondaForm(auto_id=False)
>>> print f
<tr><th>Name:</th><td><input type="text" name="name" value="Honda Accord Wagon" maxlength="50" /></td></tr>
<tr><th>Steering:</th><td><select name="steering">
<option value="left">Left steering wheel</option>
<option value="right" selected="selected">Right steering wheel</option>
</select></td></tr>
<tr><th>Fuel:</th><td><select name="fuel">
<option value="gas" selected="selected">Gasoline</option>
<option value="diesel">Diesel</option>
<option value="other">Other</option>
</select></td></tr>
<tr><th>Transmission:</th><td><select name="transmission">
<option value="">---------</option>
<option value="at" selected="selected">Automatic</option>
<option value="mt">Manual</option>
<option value="cvt">CVT</option>
</select><br />Leave empty if not applicable.</td></tr>
"""}