# Django 2.2.9.dev20191202104323 文档

# django.forms.renderers 源代码

    import functools
    from pathlib import Path

    from django.conf import settings
    from django.template.backends.django import DjangoTemplates
    from django.template.loader import get_template
    from django.utils.functional import cached_property
    from django.utils.module_loading import import_string

    try:
        from django.template.backends.jinja2 import Jinja2
    except ImportError:
        def Jinja2(params):
            raise ImportError("jinja2 isn't installed")

    ROOT = Path(__file__).parent

    @functools.lru_cache()
    def get_default_renderer():
        renderer_class = import_string(settings.FORM_RENDERER)
        return renderer_class()

    class BaseRenderer:
        def get_template(self, template_name):
            raise NotImplementedError('subclasses must implement get_template()')

        def render(self, template_name, context, request=None):
            template = self.get_template(template_name)
            return template.render(context, request=request).strip()

    class EngineMixin:
        def get_template(self, template_name):
            return self.engine.get_template(template_name)

        @cached_property
        def engine(self):
            return self.backend({
                'APP_DIRS': True,
                'DIRS': [str(ROOT / self.backend.app_dirname)],
                'NAME': 'djangoforms',
                'OPTIONS': {},
            })

    class DjangoTemplates(EngineMixin, BaseRenderer):
        """
        Load Django templates from the built-in widget templates in
        django/forms/templates and from apps' 'templates' directory.
        """
        backend = DjangoTemplates

    class Jinja2(EngineMixin, BaseRenderer):
        """
        Load Jinja2 templates from the built-in widget templates in
        django/forms/jinja2 and from apps' 'jinja2' directory.
        """
        backend = Jinja2

    class TemplatesSetting(BaseRenderer):
        """
        Load templates using template.loader.get_template() which is configured
        based on settings.TEMPLATES.
        """
        def get_template(self, template_name):
            return get_template(template_name)