Could anyone provide a simple example, so that I understand the basic idioms of how this is done? I can't find any helpful documentation that I can understand on the topic.
To provide a little more context, I'd like to create my own radio buttons, that are rendered in a particular way.
I'm just looking for a very simple example to help me understand this concept.
It's hard to tell what you mean by "a very simple example". Here is a very simple example:
from django.forms.widgets import Input
class TelInput(Input):
input_type = 'tel'
But I don't think this will help you much.
If you are looking for examples, best is still to check out django source code.
I think this should be sufficient to understand how it works:
from django.utils.encoding import force_text
from django.utils.html import format_html
from django.forms.utils import flatatt
class Widget(...):
def __init__(self, attrs=None):
if attrs is not None:
self.attrs = attrs.copy()
else:
self.attrs = {}
def subwidgets(self, name, value, attrs=None, choices=()):
"""
Yields all "subwidgets" of this widget. Used only by RadioSelect to
allow template access to individual <input type="radio"> buttons.
Arguments are the same as for render().
"""
yield SubWidget(self, name, value, attrs, choices)
def render(self, name, value, attrs=None):
"""
Returns this Widget rendered as HTML, as a Unicode string.
The 'value' given is not guaranteed to be valid input, so subclass
implementations should program defensively.
"""
raise NotImplementedError('subclasses of Widget must provide a render() method')
def build_attrs(self, extra_attrs=None, **kwargs):
"Helper function for building an attribute dictionary."
attrs = dict(self.attrs, **kwargs)
if extra_attrs:
attrs.update(extra_attrs)
return attrs
def value_from_datadict(self, data, files, name):
"""
Given a dictionary of data and this widget's name, returns the value
of this widget. Returns None if it's not provided.
"""
return data.get(name)
class Input(Widget):
"""
Base class for all <input> widgets (except type='checkbox' and
type='radio', which are special).
"""
input_type = None # Subclasses must define this.
def format_value(self, value):
if self.is_localized:
return formats.localize_input(value)
return value
def render(self, name, value, attrs=None):
if value is None:
value = ''
final_attrs = self.build_attrs(attrs, type=self.input_type, name=name)
if value != '':
# Only add the 'value' attribute if a value is non-empty.
final_attrs['value'] = force_text(self.format_value(value))
return format_html('<input{} />', flatatt(final_attrs))
Most relevant methods are render() that renders the widget as HTML code, and value_from_datadict() that extracts the value of the widget from the POST data dictionary.
