我正在对包含以下类型的转发的表调用dask.dataframe.read\u sql\u table（）

Table "public.includes_retweets"
         Column          |  Type   | 
-------------------------+---------+
 level_0                 | integer |
 reshared_message_id     | integer |
 resharing_message_id    | integer |
 resharing_user_id       | integer |
 index                   | integer |
 original_message_id     | integer |
 political_link          | text    |
 link_slant              | text    |
 political_phrases       | text[]  |
 phrase_slant            | text    |
 slant_overall           | text    |
 original_user_id        | integer |
 intermediate_user_id    | integer |
 intermediate_message_id | integer |

当我没有指定meta参数时，dask将数据读入为

level_0 reshared_message_id resharing_message_id resharing_user_id  index  original_message_id  political_link  link_slant                                  political_phrases phrase_slant slant_overall  original_user_id  intermediate_user_id
intermediate_message_id                                                                                                                                                                                                                                                  
8135                           0           209789789                 8135         209780224     26            209780224  news.yahoo.com    democrat                                               None         None      democrat           3178208             209780224
8135                           1           209789789                 8135         209780224     27            209780224  news.yahoo.com    democrat                                               None         None      democrat           3178208             209780224
1785557                        0           209829307              1785557         209828919     94            209828919            None        None         [{, ", T, R, U, M, P,  , 2, 0, 2, 0, ", }]   republican    republican            237437             209828919

在dask返回的内容中，我希望第3行有[{trump2020}]表示政治短语。
如何正确指定meta？我试过了https://github.com/dask/dask/issues/4723)

meta3={'level_0': [1], 'reshared_message_id': [1], 'resharing_message_id': [1], 'resharing_user_id': [1], 'index': [1], 'original_message_id': [1], 'political_link': ["Text"], 'link_slant': ["Text"], 'political_phrases': [["Text", "secondText"]], 'phrase_slant': ["Text"], 'slant_overall': ["Text"], 'original_user_id': [1], 'intermediate_user_id': [1], 'intermediate_message_id': [1]}
meta4 = pd.DataFrame(meta3)[0:0]

和（在指定列类型的列中创建空Dataframe）

dtypes=np.dtype([('level_0',int), ('reshared_message_id',int), ('resharing_message_id',int) , ('resharing_user_id',int) , ('index',int) , ('original_message_id',int) , ('political_link',str), ('link_slant',str) ,('political_phrases', np.str_), ('phrase_slant', str), ('slant_overall', str), ('original_user_id',int), ('intermediate_user_id',int) , ('intermediate_message_id',int),])
meta4 = np.empty(0, dtype=dtypes)

然后把这些值或这些值的变化传递给这里的meta

dask.dataframe.read_sql_table(includes_retweets_table, db_uri, meta=meta4, index_col='intermediate_message_id', npartitions=12)

当我打印从dask.dataframe.read\ sql\ table（）返回的内容时，我得到

Dask DataFrame Structure:
               level_0 reshared_message_id resharing_message_id resharing_user_id  index original_message_id political_link link_slant political_phrases phrase_slant slant_overall original_user_id intermediate_user_id intermediate_message_id
npartitions=12                                                                                                                                                                                                                                   
8135.0           int64               int64                int64             int64  int64               int64         object     object            object       object        object            int64                int64                   int64
17494966.0         ...                 ...                  ...               ...    ...                 ...            ...        ...               ...          ...           ...              ...                  ...                     ...
...                ...                 ...                  ...               ...    ...                 ...            ...        ...               ...          ...           ...              ...                  ...                     ...
192363276.0        ...                 ...                  ...               ...    ...                 ...            ...        ...               ...          ...           ...              ...                  ...                     ...
209850107.0        ...                 ...                  ...               ...    ...                 ...            ...        ...               ...          ...           ...              ...                  ...                     ...

当我尝试执行.compute（）时，我得到下面的错误

distributed.worker - WARNING -  Compute Failed
Function:  execute_task
args:      ((<function check_meta at 0x7f8b040ca290>, (<function apply at 0x7f8b02de3830>, <function _read_sql_chunk at 0x7f8b041dc0e0>, [<sqlalchemy.sql.selectable.Select at 0x7f8b04353710; Select object>, 'postgresql+psycopg2://postgres:password@localhost:5432/stocktwits', Empty DataFrame
Columns: [level_0, reshared_message_id, resharing_message_id, resharing_user_id, index, original_message_id, political_link, link_slant, political_phrases, phrase_slant, slant_overall, original_user_id, intermediate_user_id, intermediate_message_id]
Index: []], (<class 'dict'>, [['engine_kwargs', (<class 'dict'>, [])], ['index_col', 'intermediate_message_id']])), Empty DataFrame
Columns: [level_0, reshared_message_id, resharing_message_id, resharing_user_id, index, original_message_id, political_link, link_slant, political_phrases, phrase_slant, slant_overall, original_user_id, intermediate_user_id, intermediate_message_id]
Index: [], 'from_delayed'))
kwargs:    {}
Exception: KeyError('Only a column name can be used for the key in a dtype mappings argument.')

Traceback (most recent call last):
  File "interpreterScript.py", line 359, in <module>
    main()
  File "interpreterScript.py", line 162, in main
    print(includes_retweets.compute())
  File "/opt/anaconda3/lib/python3.7/site-packages/dask/base.py", line 166, in compute
    (result,) = compute(self, traverse=False,**kwargs)
  File "/opt/anaconda3/lib/python3.7/site-packages/dask/base.py", line 444, in compute
    results = schedule(dsk, keys,**kwargs)
  File "/opt/anaconda3/lib/python3.7/site-packages/distributed/client.py", line 2682, in get
    results = self.gather(packed, asynchronous=asynchronous, direct=direct)
  File "/opt/anaconda3/lib/python3.7/site-packages/distributed/client.py", line 1982, in gather
    asynchronous=asynchronous,
  File "/opt/anaconda3/lib/python3.7/site-packages/distributed/client.py", line 832, in sync
    self.loop, func, *args, callback_timeout=callback_timeout,**kwargs
  File "/opt/anaconda3/lib/python3.7/site-packages/distributed/utils.py", line 339, in sync
    raise exc.with_traceback(tb)
  File "/opt/anaconda3/lib/python3.7/site-packages/distributed/utils.py", line 323, in f
    result[0] = yield future
  File "/opt/anaconda3/lib/python3.7/site-packages/tornado/gen.py", line 735, in run
    value = future.result()
  File "/opt/anaconda3/lib/python3.7/site-packages/distributed/client.py", line 1841, in _gather
    raise exception.with_traceback(traceback)
  File "/opt/anaconda3/lib/python3.7/site-packages/dask/utils.py", line 31, in apply
    return func(*args,**kwargs)
  File "/opt/anaconda3/lib/python3.7/site-packages/dask/dataframe/io/sql.py", line 216, in _read_sql_chunk
    return df.astype(meta.dtypes.to_dict(), copy=False)
  File "/opt/anaconda3/lib/python3.7/site-packages/pandas/core/generic.py", line 5857, in astype
    "Only a column name can be used for the "
KeyError: 'Only a column name can be used for the key in a dtype mappings argument.'

这个错误对我来说没有意义，因为我包含了表include\u retweets中所有具有正确数据类型的列名。