'Get the template source, filename and reload helper for a template.
It\'s passed the environment and template name and has to return a
tuple in the form ``(source, filename, uptodate)`` or raise a
`TemplateNotFound` error if it can\'t locate the template.
The source part of the returned tuple must be the source of the
template as unicode string or a ASCII bytestring.  The filename should
be the name of the file on the filesystem if it was loaded from there,
otherwise `None`.  The filename is used by python for the tracebacks
if no loader extension is used.
The last item in the tuple is the `uptodate` function.  If auto
reloading is enabled it\'s always called to check if the template
changed.  No arguments are passed so the function must store the
old state somewhere (for example in a closure).  If it returns `False`
the template will be reloaded.'

def get_source(self, environment, template):

    raise TemplateNotFound(template)
