code: def _edge_list_to_dataframe(ls, src_column_name, dst_column_name):
      
      assert HAS_PANDAS, 'Cannot use dataframe because Pandas is not available or version is too low.'
      cols = reduce(set.union, (set(e.attr.keys()) for e in ls))
      df = pd.DataFrame({
          src_column_name: [e.src_vid for e in ls],
          dst_column_name: [e.dst_vid for e in ls]})
      for c in cols:
          df[c] = [e.attr.get(c) for e in ls]
      return df
docs: Convert a list of edges into dataframe.