django-bootstrap4 errors at fields

django-bootstrap4-field-errors.py

from bootstrap4.renderers import FormRenderer, FieldRenderer
from bootstrap4.text import text_value


class FieldErrorFormRenderer(FormRenderer):
	"""
	Adapted version of Bootstrap 4 FormRenderer, that shows error messages
	at the field, rather than at the top.
	"""
	def _render(self):
		return self.render_errors('non_fields') + self.render_fields()


class WithErrorFieldRenderer(FieldRenderer):
	"""
	Adapted version of Bootstrap 4 FieldRenderer, that shows error messages
	at the field, rather than at the top.
	"""

	def add_field_errors(self, html):
		if not self.field.errors:
			return html
		errhtml = '<div class="{0:s} alert alert-danger" role="alert">'.format(self.error_css_class)
		for error in self.field.errors:
			errhtml += '<p>' + error + '</p>'
		errhtml += '</div>'
		html += errhtml
		return html

	def _render(self):
		# See if we're not excluded
		if self.field.name in self.exclude.replace(' ', '').split(','):
			return ''
		# Hidden input requires no special treatment
		if self.field.is_hidden:
			return text_value(self.field)
		# Render the widget
		self.add_widget_attrs()
		html = self.field.as_widget(attrs=self.widget.attrs)
		self.restore_widget_attrs()
		# Start post render
		html = self.post_widget_render(html)
		html = self.wrap_widget(html)
		html = self.make_input_group(html)
		html = self.append_to_field(html)
		html = self.add_field_errors(html)
		html = self.wrap_field(html)
		html = self.add_label(html)
		html = self.wrap_label_and_field(html)
		return html

With these settings:

BOOTSTRAP4 = dict(
    form_renderers=dict(
        default='appname.form_renderer.FieldErrorFormRenderer',
    ),
    field_renderers=dict(
        default='appname.form_renderer.WithErrorFieldRenderer',
    ),
)