     dfs[i] = pd.read_csv(StringIO('\n'.join(lines[0:])))  df = pd.concat(dfs, keys=keys) df = df.set_index(['USER_ID', 'USER_NAME'], append=True).unstack(0)  df.index = df.index.droplevel(0) df.columns = df.columns.droplevel(0)  df = df.stack().unstack()