python – Jinja2模板编译信息

我用来获取包含文件和代码的完整堆栈跟踪的代码：

def _generate_django_exception(e,source=None):
    '''Generate a Django exception from a Jinja source'''
    from django.views.debug import linebreak_iter

    if source:
        exception = DjangoTemplateSyntaxError(e.message)
        exception_dict = e.__dict__
        del exception_dict['source']

        '''Fetch the entire template in a string'''
        template_string = source[0].reload()

        '''Get the line number from the error message,if available'''
        match = re.match('.* at (d+)$',e.message)

        start_index = 0
        stop_index = 0
        if match:
            '''Convert the position found in the stacktrace to a position
            the Django template debug system can use'''
            position = int(match.group(1)) + source[1][0] + 1

            for index in linebreak_iter(template_string):
                if index >= position:
                    stop_index = min(index,position + 3)
                    start_index = min(index,position - 2)
                    break
                start_index = index

        else:
            '''So there wasn't a matching error message,in that case we
            simply have to highlight the entire line instead of the specific
            words'''
            ignore_lines = 0
            for i,index in enumerate(linebreak_iter(template_string)):
                if source[1][0] > index:
                    ignore_lines += 1

                if i - ignore_lines == e.lineno:
                    stop_index = index
                    break

                start_index = index

        '''Convert the positions to a source that is compatible with the
        Django template debugger'''
        source = source[0],(
            start_index,stop_index,)
    else:
        '''No source available so we let Django fetch it for us'''
        lineno = e.lineno - 1
        template_string,source = django_loader.find_template_source(e.name)
        exception = DjangoTemplateSyntaxError(e.message)

        '''Find the positions by the line number given in the exception'''
        start_index = 0
        for i in range(lineno):
            start_index = template_string.index('n',start_index + 1)

        source = source,(
            start_index + 1,template_string.index('n',start_index + 1) + 1,)

    exception.source = source
    return exception

实际的模板标签：

class Template(_Jinja2Template):
    """Fixes the incompabilites between Jinja2's template class and
    Django's.                                                                                                                                                                                        

    The end result should be a class that renders Jinja2 templates but
    is compatible with the interface specfied by Django.                                                                                                                                             

    This includes flattening a ``Context`` instance passed to render
    and making sure that this class will automatically use the global
    coffin environment.
    """

    def __new__(cls,template_string,origin=None,name=None,source=None):
        # We accept the "origin" and "name" arguments,but discard them
        # right away - Jinja's Template class (apparently) stores no
        # equivalent information.
        from coffin.common import env

        try:
            return env.from_string(template_string,template_class=cls)
        except JinjaTemplateSyntaxError,e:
            raise _generate_django_exception(e,source)

    def __iter__(self):
        # TODO: Django allows iterating over the templates nodes. Should
        # be parse ourself and iterate over the AST?
        raise NotImplementedError()

    def render(self,context=None):
        """Differs from Django's own render() slightly in that makes the
        ``context`` parameter optional. We try to strike a middle ground
        here between implementing Django's interface while still supporting
        Jinja's own call syntax as well.
        """
        if not context:
            context = {}
        else:
            context = dict_from_django_context(context)

        try:
            return super(Template,self).render(context)
        except JinjaTemplateSyntaxError,e:
            raise _generate_django_exception(e)

def dict_from_django_context(context):
    """Flattens a Django :class:`django.template.context.Context` object.
    """
    if isinstance(context,DjangoContext):
        dict_ = {}
        # Newest dicts are up front,so update from oldest to newest.
        for subcontext in reversed(list(context)):
            dict_.update(dict_from_django_context(subcontext))
        return dict_
    else:
        return context