groupby creation

When creating document from another one
but all lines don't go necessary into the same document

   def create(self):
       lines = self.get_lines()
       for key, lines in groupby(lines, key=self.key):
           doc = Doc(**dict(key))
           doc.lines = list(lines)

   def key(self, line):
       return (
            ('key', line.value),
            ...
            )