Horizon Forms

Horizon ships with some very useful base form classes, form fields, class-based views, and javascript helpers which streamline most of the common tasks related to form handling.

Form Classes

class horizon.forms.base.DateForm(*args, **kwargs)[source]

A simple form for selecting a range of time.

class horizon.forms.base.SelfHandlingForm(request, *args, **kwargs)[source]

A base Form class which includes processing logic in its subclasses.


Adds an error to the form’s error dictionary after validation based on problems reported via the API. This is useful when you wish for API errors to appear as errors on the form rather than using the messages framework.


Sets a warning on the form.

Unlike NON_FIELD_ERRORS, this doesn’t fail form validation.

Form Fields

class horizon.forms.fields.DynamicChoiceField(add_item_link=None, add_item_link_args=None, *args, **kwargs)[source]

A subclass of ChoiceField with additional properties that make dynamically updating its elements easier.

Notably, the field declaration takes an extra argument, add_item_link which may be a string or callable defining the URL that should be used for the “add” link associated with the field.


alias of DynamicSelectWidget

class horizon.forms.fields.DynamicSelectWidget(attrs=None, choices=())[source]

A subclass of the Select widget which renders extra attributes for use in callbacks to handle dynamic changes to the available choices.

class horizon.forms.fields.DynamicTypedChoiceField(add_item_link=None, add_item_link_args=None, *args, **kwargs)[source]

Simple mix of DynamicChoiceField and TypedChoiceField.

class horizon.forms.fields.IPField(*args, **kwargs)[source]

Form field for entering IP/range values, with validation. Supports IPv4/IPv6 in the format: .. xxx.xxx.xxx.xxx .. xxx.xxx.xxx.xxx/zz .. ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff .. ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff/zz and all compressed forms. Also the short forms are supported: xxx/yy xxx.xxx/yy


Specifies which IP version to validate, valid values are 1 (fields.IPv4), 2 (fields.IPv6) or both - 3 (fields.IPv4 | fields.IPv6). Defaults to IPv4 (1)


Boolean flag to validate subnet masks along with IP address. E.g:

Subnet range limitation, e.g. 16
That means the input mask will be checked to be in the range
16:max_value. Useful to limit the subnet ranges
to A/B/C-class networks.
class horizon.forms.fields.MultiIPField(*args, **kwargs)[source]

Extends IPField to allow comma-separated lists of addresses.

class horizon.forms.fields.SelectWidget(attrs=None, choices=(), data_attrs=(), transform=None, transform_html_attrs=None)[source]

Customizable select widget, that allows to render data-xxx attributes from choices. This widget also allows user to specify additional html attributes for choices.


Specifies object properties to serialize as data-xxx attribute. If passed (‘id’, ), this will be rendered as: <option data-id=”123”>option_value</option> where 123 is the value of choice_value.id


A callable used to render the display value from the option object.


A callable used to render additional HTML attributes for the option object. It returns a dictionary containing the html attributes and their values. For example, to define a title attribute for the choices:

helpText = { 'Apple': 'This is a fruit',
          'Carrot': 'This is a vegetable' }

def get_title(data):
    text = helpText.get(data, None)
    if text:
        return {'title': text}
        return {}


widget=forms.SelectWidget( attrs={'class': 'switchable',
                                 'data-slug': 'source'},
                        transform_html_attrs=get_title )

self.fields[<field name>].choices =
class horizon.forms.fields.ThemableCheckboxInput(attrs=None, check_test=None)[source]

A subclass of the Checkbox widget which renders extra markup to allow a custom checkbox experience.

Form Views

class horizon.forms.views.ModalBackdropMixin(*args, **kwargs)[source]

This mixin class is to be used for together with ModalFormView and WorkflowView classes to augment them with modal_backdrop context data.

class horizon.forms.views.ModalFormView(*args, **kwargs)[source]

The main view class from which all views which handle forms in Horizon should inherit. It takes care of all details with processing SelfHandlingForm classes, and modal concerns when the associated template inherits from horizon/common/_modal_form.html.

Subclasses must define a form_class and template_name attribute at minimum.

See Django’s documentation on the FormView class for more details.


For dynamic insertion of resources created in modals, this method returns the display name of the created object. Defaults to returning the name attribute.


For dynamic insertion of resources created in modals, this method returns the id of the created object. Defaults to returning the id attribute.

Forms Javascript

Switchable Fields

By marking fields with the "switchable" and "switched" classes along with defining a few data attributes you can programmatically hide, show, and rename fields in a form.

The triggers are fields using a select input widget, marked with the “switchable” class, and defining a “data-slug” attribute. When they are changed, any input with the "switched" class and defining a "data-switch-on" attribute which matches the select input’s "data-slug" attribute will be evaluated for necessary changes. In simpler terms, if the "switched" target input’s "switch-on" matches the "slug" of the "switchable" trigger input, it gets switched. Simple, right?

The "switched" inputs also need to define states. For each state in which the input should be shown, it should define a data attribute like the following: data-<slug>-<value>="<desired label>". When the switch event happens the value of the "switchable" field will be compared to the data attributes and the correct label will be applied to the field. If a corresponding label for that value is not found, the field will be hidden instead.

A simplified example is as follows:

source = forms.ChoiceField(
        ('cidr', _('CIDR')),
        ('sg', _('Security Group'))
        'class': 'switchable',
        'data-slug': 'source'

cidr = fields.IPField(
        'class': 'switched',
        'data-switch-on': 'source',
        'data-source-cidr': _('CIDR')

security_group = forms.ChoiceField(
    label=_('Security Group'),
        'class': 'switched',
        'data-switch-on': 'source',
        'data-source-sg': _('Security Group')

That code would create the "switchable" control field source, and the two "switched" fields cidr and security group which are hidden or shown depending on the value of source.

NOTE: A field can only safely define one slug in its "switch-on" attribute. While switching on multiple fields is possible, the behavior is very hard to predict due to the events being fired from the various switchable fields in order. You generally end up just having it hidden most of the time by accident, so it’s not recommended. Instead just add a second field to the form and control the two independently, then merge their results in the form’s clean or handle methods at the end.

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