我正在尝试将一个大型数据集（1300万行）从mysql数据库读入pandas（0.17.1）。根据网上的一个建议，我使用了 chunksize 参数来执行此操作。

db = pymysql.connect(HOST,           # localhost
                     port=PORT,      # port
                     user=USER,      # username
                     password=PASSW, # password
                     db=DATABASE)    # name of the data base
df = pd.DataFrame()
query = "SELECT * FROM `table`;"
for chunks in pd.read_sql(query, con=db, chunksize=100000):
    df = df.append(chunks)

但每次我做这件事都会有麻烦 TypeError: Argument 'rows' has incorrect type (expected list, got tuple) 错误。
当我没有使用chunksize参数，因此没有生成generator对象时，这就起作用了。我可以看到mysql正在返回一个 tuple-of-tuples 而不是 list-of-tuples .
所以，我的问题是，为什么查询在正常情况下工作，我该怎么做才能确保我从数据库中得到一个元组列表，这样我就可以使用它了？
完整的回溯看起来像这样

TypeError                                 Traceback (most recent call last)
<ipython-input-20-efe94dcd2c70> in <module>()
      8 df_horses = pd.DataFrame()
      9 query = "SELECT * FROM `horses`;"
---> 10 for chunks in pd.read_sql(query, con=db, chunksize=10000):
     11     df_horses = df_horses.append(chunks)
     12 print df_horses.shape
/home/ubuntu/anaconda2/lib/python2.7/site-packages/pandas/io/sql.pyc in _query_iterator(cursor, chunksize, columns, index_col, coerce_float, parse_dates)
   1563                 yield _wrap_result(data, columns, index_col=index_col,
   1564                                    coerce_float=coerce_float,
-> 1565                                    parse_dates=parse_dates)
   1566 
   1567     def read_query(self, sql, index_col=None, coerce_float=True, params=None,
/home/ubuntu/anaconda2/lib/python2.7/site-packages/pandas/io/sql.pyc in _wrap_result(data, columns, index_col, coerce_float, parse_dates)
    135 
    136     frame = DataFrame.from_records(data, columns=columns,
--> 137                                    coerce_float=coerce_float)
    138 
    139     _parse_date_columns(frame, parse_dates)
/home/ubuntu/anaconda2/lib/python2.7/site-packages/pandas/core/frame.pyc in from_records(cls, data, index, exclude, columns, coerce_float, nrows)
    967         else:
    968             arrays, arr_columns = _to_arrays(data, columns,
--> 969                                              coerce_float=coerce_float)
    970 
    971             arr_columns = _ensure_index(arr_columns)
/home/ubuntu/anaconda2/lib/python2.7/site-packages/pandas/core/frame.pyc in _to_arrays(data, columns, coerce_float, dtype)
   5277     if isinstance(data[0], (list, tuple)):
   5278         return _list_to_arrays(data, columns, coerce_float=coerce_float,
-> 5279                                dtype=dtype)
   5280     elif isinstance(data[0], collections.Mapping):
   5281         return _list_of_dict_to_arrays(data, columns,
/home/ubuntu/anaconda2/lib/python2.7/site-packages/pandas/core/frame.pyc in _list_to_arrays(data, columns, coerce_float, dtype)
   5355 def _list_to_arrays(data, columns, coerce_float=False, dtype=None):
   5356     if len(data) > 0 and isinstance(data[0], tuple):
-> 5357         content = list(lib.to_object_array_tuples(data).T)
   5358     else:
   5359         # list of lists
TypeError: Argument 'rows' has incorrect type (expected list, got tuple)