# Django 2.2.9.dev20191202104323 文档

# django.template.backends.jinja2 源代码

    import jinja2

    from django.conf import settings
    from django.template import TemplateDoesNotExist, TemplateSyntaxError
    from django.utils.functional import cached_property
    from django.utils.module_loading import import_string

    from .base import BaseEngine

    class Jinja2(BaseEngine):

        app_dirname = 'jinja2'

        def __init__(self, params):
            params = params.copy()
            options = params.pop('OPTIONS').copy()
            super().__init__(params)

            self.context_processors = options.pop('context_processors', [])

            environment = options.pop('environment', 'jinja2.Environment')
            environment_cls = import_string(environment)

            if 'loader' not in options:
                options['loader'] = jinja2.FileSystemLoader(self.template_dirs)
            options.setdefault('autoescape', True)
            options.setdefault('auto_reload', settings.DEBUG)
            options.setdefault('undefined',
                               jinja2.DebugUndefined if settings.DEBUG else jinja2.Undefined)

            self.env = environment_cls(**options)

        def from_string(self, template_code):
            return Template(self.env.from_string(template_code), self)

        def get_template(self, template_name):
            try:
                return Template(self.env.get_template(template_name), self)
            except jinja2.TemplateNotFound as exc:
                raise TemplateDoesNotExist(exc.name, backend=self) from exc
            except jinja2.TemplateSyntaxError as exc:
                new = TemplateSyntaxError(exc.args)
                new.template_debug = get_exception_info(exc)
                raise new from exc

        @cached_property
        def template_context_processors(self):
            return [import_string(path) for path in self.context_processors]

    class Template:

        def __init__(self, template, backend):
            self.template = template
            self.backend = backend
            self.origin = Origin(
                name=template.filename, template_name=template.name,
            )

        def render(self, context=None, request=None):
            from .utils import csrf_input_lazy, csrf_token_lazy
            if context is None:
                context = {}
            if request is not None:
                context['request'] = request
                context['csrf_input'] = csrf_input_lazy(request)
                context['csrf_token'] = csrf_token_lazy(request)
                for context_processor in self.backend.template_context_processors:
                    context.update(context_processor(request))
            return self.template.render(context)

    class Origin:
        """
        A container to hold debug information as described in the template API
        documentation.
        """
        def __init__(self, name, template_name):
            self.name = name
            self.template_name = template_name

    def get_exception_info(exception):
        """
        Format exception information for display on the debug page using the
        structure described in the template API documentation.
        """
        context_lines = 10
        lineno = exception.lineno
        lines = list(enumerate(exception.source.strip().split("\n"), start=1))
        during = lines[lineno - 1][1]
        total = len(lines)
        top = max(0, lineno - context_lines - 1)
        bottom = min(total, lineno + context_lines)

        return {
            'name': exception.filename,
            'message': exception.message,
            'source_lines': lines[top:bottom],
            'line': lineno,
            'before': '',
            'during': during,
            'after': '',
            'total': total,
            'top': top,
            'bottom': bottom,
        }