code: def duplicate_files(self):
          '''
          Search for duplicates of submission file uploads for this assignment.
          This includes the search in other course, whether inactive or not.
          Returns a list of lists, where each latter is a set of duplicate submissions
          with at least on of them for this assignment
          '''
          result=list()
          files = SubmissionFile.valid_ones.order_by('md5')
  
          for key, dup_group in groupby(files, lambda f: f.md5):
              file_list=[entry for entry in dup_group]
              if len(file_list)>1:
                  for entry in file_list:
                      if entry.submissions.filter(assignment=self).count()>0:
                          result.append([key, file_list])
                          break
          return resulf duplicate_files(self):
          '''
          Search for duplicates of submission file uploads for this assignment.
          This includes the search in other course, whether inactive or not.
          Returns a list of lists, where each latter is a set of duplicate submissions
          with at least on of them for this assignment
          '''
          result=list()
          files = SubmissionFile.valid_ones.order_by('md5')
  
          for key, dup_group in groupby(files, lambda f: f.md5):
              file_list=[entry for entry in dup_group]
              if len(file_list)>1:
                  for entry in file_list:
                      if entry.submissions.filter(assignment=self).count()>0:
                          result.append([key, file_list])
                          break
          return result
docs: Search for duplicates of submission file uploads for this assignment.
          This includes the search in other course, whether inactive or not.
          Returns a list of lists, where each latter is a set of duplicate submissions
          with at least on of them for this assignment