This can be done using a custom template filter. Consider rendering your form this way:

<form action="/contact/" method="post">
  {{ form.non_field_errors }}
  <div class="fieldWrapper">
    {{ form.subject.errors }}
    {{ form.subject.label_tag }}
    {{ form.subject }}
    <span class="helptext">{{ form.subject.help_text }}</span>
  </div>
</form>

form.subject is an instance of BoundField which has the as_widget() method.

You can create a custom filter addclass in my_app/templatetags/myfilters.py:

from django import template

register = template.Library()

@register.filter(name='addclass')
def addclass(value, arg):
    return value.as_widget(attrs={'class': arg})

And then apply your filter:

{% load myfilters %}

<form action="/contact/" method="post">
  {{ form.non_field_errors }}
  <div class="fieldWrapper">
    {{ form.subject.errors }}
    {{ form.subject.label_tag }}
    {{ form.subject|addclass:'MyClass' }}
    <span class="helptext">{{ form.subject.help_text }}</span>
  </div>
</form>

form.subjects will then be rendered with the MyClass CSS class.

If you don't want to add any code to the form (as mentioned in the comments to @shadfc's Answer), it is certainly possible, here are two options.

First, you just reference the fields individually in the HTML, rather than the entire form at once:

<form action="" method="post">
    <ul class="contactList">
        <li id="subject" class="contact">{{ form.subject }}</li>
        <li id="email" class="contact">{{ form.email }}</li>
        <li id="message" class="contact">{{ form.message }}</li>
    </ul>
    <input type="submit" value="Submit">
</form>

(Note that I also changed it to a unsorted list.)

Second, note in the docs on outputting forms as HTML, Django:

The Field id, is generated by prepending 'id_' to the Field name. The id attributes and tags are included in the output by default.

All of your form fields already have a unique id. So you would reference id_subject in your CSS file to style the subject field. I should note, this is how the form behaves when you take the default HTML, which requires just printing the form, not the individual fields:

<ul class="contactList">
    {{ form }}  # Will auto-generate HTML with id_subject, id_email, email_message 
    {{ form.as_ul }} # might also work, haven't tested
</ul>

See the previous link for other options when outputting forms (you can do tables, etc).

Note - I realize this isn't the same as adding a class to each element (if you added a field to the Form, you'd need to update the CSS also) - but it's easy enough to reference all of the fields by id in your CSS like this:

#id_subject, #id_email, #email_message 
{color: red;}

Per this blog post, you can add css classes to your fields using a custom template filter.

from django import template
register = template.Library()

@register.filter(name='addcss')
def addcss(field, css):
    return field.as_widget(attrs={"class":css})

Put this in your app's templatetags/ folder and you can now do

{{field|addcss:"form-control"}}

You can do like this:

class ContactForm(forms.Form):
    subject = forms.CharField(max_length=100)
    subject.widget.attrs.update({'id' : 'your_id'})

Hope that works.

Ignas

You could use this library: https://pypi.python.org/pypi/django-widget-tweaks

It allows you to do the following:

{% load widget_tweaks %}
<!-- add 2 extra css classes to field element -->
{{ form.title|add_class:"css_class_1 css_class_2" }}

Write your form like:

    class MyForm(forms.Form):
         name = forms.CharField(widget=forms.TextInput(attr={'class':'name'}),label="Your Name")
         message = forms.CharField(widget=forms.Textarea(attr={'class':'message'}), label="Your Message")

In your HTML field do something like:

{% for field in form %}
      <div class="row">
        <label for="{{ field.name}}">{{ field.label}}</label>{{ field }}
     </div>
{% endfor %}

Then in your CSS write something like:

.name{
      /* you already have this class so create it's style form here */
}
.message{
      /* you already have this class so create it's style form here */
}
label[for='message']{
      /* style for label */
}

Hope this answer is worth a try! Note you must have written your views to render the HTML file that contains the form.

You can do:

<form action="" method="post">
    <table>
        {% for field in form %}
        <tr><td>{{field}}</td></tr>
        {% endfor %}
    </table>
    <input type="submit" value="Submit">
</form>

Then you can add classes/id's to for example the <td> tag. You can of course use any others tags you want. Check Working with Django forms as an example what is available for each field in the form ({{field}} for example is just outputting the input tag, not the label and so on).

Didn't see this one really...

https://docs.djangoproject.com/en/1.8/ref/forms/api/#more-granular-output

More granular output

The as_p(), as_ul() and as_table() methods are simply shortcuts for lazy developers – they’re not the only way a form object can be displayed.

class BoundField Used to display HTML or access attributes for a single field of a Form instance.

The str() (unicode on Python 2) method of this object displays the HTML for this field.

To retrieve a single BoundField, use dictionary lookup syntax on your form using the field’s name as the key:

>>> form = ContactForm()
>>> print(form['subject'])
<input id="id_subject" type="text" name="subject" maxlength="100" />

To retrieve all BoundField objects, iterate the form:

>>> form = ContactForm()
>>> for boundfield in form: print(boundfield)
<input id="id_subject" type="text" name="subject" maxlength="100" />
<input type="text" name="message" id="id_message" />
<input type="email" name="sender" id="id_sender" />
<input type="checkbox" name="cc_myself" id="id_cc_myself" />

The field-specific output honors the form object’s auto_id setting:

>>> f = ContactForm(auto_id=False)
>>> print(f['message'])
<input type="text" name="message" />
>>> f = ContactForm(auto_id='id_%s')
>>> print(f['message'])
<input type="text" name="message" id="id_message" />

One solution is to use JavaScript to add the required CSS classes after the page is ready. For example, styling django form output with bootstrap classes (jQuery used for brevity):

<script type="text/javascript">
    $(document).ready(function() {
        $('#some_django_form_id').find("input[type='text'], select, textarea").each(function(index, element) {
            $(element).addClass("form-control");
        });
    });
</script>

This avoids the ugliness of mixing styling specifics with your business logic.

You may not need to override your form class' __init__, because Django sets name & id attributes in the HTML inputs. You can have CSS like this:

form input[name='subject'] {
    font-size: xx-large;
}

There is a very easy to install and great tool made for Django that I use for styling and it can be used for every frontend framework like Bootstrap, Materialize, Foundation, etc. It is called widget-tweaks Documentation: Widget Tweaks

1. You can use it with Django's generic views
2. Or with your own forms:

from django import forms

class ContactForm(forms.Form):
    subject = forms.CharField(max_length=100)
    email = forms.EmailField(required=False)
    message = forms.CharField(widget=forms.Textarea)

Instead of using default:

{{ form.as_p }} or {{ form.as_ul }}

You can edit it your own way using the render_field attribute that gives you a more html-like way of styling it like this example:

template.html

{% load widget_tweaks %}

<div class="container">
   <div class="col-md-4">
      {% render_field form.subject class+="form-control myCSSclass" placeholder="Enter your subject here" %}
   </div>
   <div class="col-md-4">
      {% render_field form.email type="email" class+="myCSSclassX myCSSclass2" %}
   </div>
   <div class="col-md-4">
      {% render_field form.message class+="myCSSclass" rows="4" cols="6" placeholder=form.message.label %}
   </div>
</div>

This library gives you the opportunity to have well separated yout front end from your backend

In Django 1.10 (possibly earlier as well) you can do it as follows.

Model:

class Todo(models.Model):
    todo_name = models.CharField(max_length=200)
    todo_description = models.CharField(max_length=200, default="")
    todo_created = models.DateTimeField('date created')
    todo_completed = models.BooleanField(default=False)

    def __str__(self):
        return self.todo_name

Form:

class TodoUpdateForm(forms.ModelForm):
    class Meta:
        model = Todo
        exclude = ('todo_created','todo_completed')

Template:

<form action="" method="post">{% csrf_token %}
    {{ form.non_field_errors }}
<div class="fieldWrapper">
    {{ form.todo_name.errors }}
    <label for="{{ form.name.id_for_label }}">Name:</label>
    {{ form.todo_name }}
</div>
<div class="fieldWrapper">
    {{ form.todo_description.errors }}
    <label for="{{ form.todo_description.id_for_label }}">Description</label>
    {{ form.todo_description }}
</div>
    <input type="submit" value="Update" />
</form>

For larger form instead of writing css classed for every field you could to this

class UserRegistration(forms.ModelForm):
   # list charfields

   class Meta:
      model = User
      fields = ('username', 'first_name', 'last_name', 'email', 'password', 'password2')

   def __init__(self, *args, **kwargs):
      super(UserRegistration, self).__init__(*args, **kwargs)
      for field in self.fields:
         self.fields[field].widget.attrs['class'] = 'form-control'

Edit: Another (slightly better) way of doing what I'm suggesting is answered here: Django form input field styling

All the above options are awesome, just thought I'd throw in this one because it's different.

If you want custom styling, classes, etc. on your forms, you can make an html input in your template that matches your form field. For a CharField, for example, (default widget is TextInput), let's say you want a bootstrap-looking text input. You would do something like this:

<input type="text" class="form-control" name="form_field_name_here">

And as long as you put the form field name matches the html name attribue, (and the widget probably needs to match the input type as well) Django will run all the same validators on that field when you run validate or form.is_valid() and

Styling other things like labels, error messages, and help text don't require much workaround because you can do something like form.field.error.as_text and style them however you want. The actual fields are the ones that require some fiddling.

I don't know if this is the best way, or the way I would recommend, but it is a way, and it might be right for someone.

Here's a useful walkthrough of styling forms and it includes most of the answers listed on SO (like using the attr on the widgets and widget tweaks). https://simpleisbetterthancomplex.com/article/2017/08/19/how-to-render-django-form-manually.html

Styling widget instances

If you want to make one widget instance look different from another, you will need to specify additional attributes at the time when the widget object is instantiated and assigned to a form field (and perhaps add some rules to your CSS files).

https://docs.djangoproject.com/en/2.2/ref/forms/widgets/

To do this, you use the Widget.attrs argument when creating the widget:

class CommentForm(forms.Form):
    name = forms.CharField(widget=forms.TextInput(attrs={'class': 'special'}))
    url = forms.URLField()
    comment = forms.CharField(widget=forms.TextInput(attrs={'size': '40'}))

You can also modify a widget in the form definition:

class CommentForm(forms.Form):
    name = forms.CharField()
    url = forms.URLField()
    comment = forms.CharField()

    name.widget.attrs.update({'class': 'special'})
    comment.widget.attrs.update(size='40')

Or if the field isn’t declared directly on the form (such as model form fields), you can use the Form.fields attribute:

class CommentForm(forms.ModelForm):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.fields['name'].widget.attrs.update({'class': 'special'})
        self.fields['comment'].widget.attrs.update(size='40')

Django will then include the extra attributes in the rendered output:

>>> f = CommentForm(auto_id=False)
>>> f.as_table()
<tr><th>Name:</th><td><input type="text" name="name" class="special" required></td></tr>
<tr><th>Url:</th><td><input type="url" name="url" required></td></tr>
<tr><th>Comment:</th><td><input type="text" name="comment" size="40" required></td></tr>

I was playing around with this solution to maintain consistency throughout the app:

def bootstrap_django_fields(field_klass, css_class):
    class Wrapper(field_klass):
        def __init__(self, **kwargs):
            super().__init__(**kwargs)

        def widget_attrs(self, widget):
            attrs = super().widget_attrs(widget)
            if not widget.is_hidden:
                attrs["class"] = css_class
            return attrs

    return Wrapper


MyAppCharField = bootstrap_django_fields(forms.CharField, "form-control")

Then you don't have to define your css classes on a form by form basis, just use your custom form field.

It's also technically possible to redefine Django's forms classes on startup like so:

forms.CharField = bootstrap_django_fields(forms.CharField, "form-control")

Then you could set the styling globally even for apps not in your direct control. This seems pretty sketchy, so I am not sure if I can recommend this.