<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_docs_sources_from_ES(self):
 """Get document sources using MGET elasticsearch API"""

        docs = [doc for doc, _, _, get_from_ES in self.doc_to_update if get_from_ES]
        if docs:
            documents = self.docman.elastic.mget(body={"docs": docs}, realtime=True)
            return iter(documents["docs"])
        else:
            return iter([])