Why do I have None ('NoneType' object is not iterable) when I expected a list?

Question

I am retrieving a list of table names using pandas.read_sql and then trying to use a "for" loop to drop tables from the retrieved list. However, I am getting a 'NoneType' object is not iterable error (although the list is not empty).

print(type(out_tables_list))
<class 'list'>
print(out_tables_list is None)
False

tables = pd.read_sql("""
SHOW TABLES IN P_SMO_INP_T
""", con=connection)

tableName = tables.tableName
out_tables = tableName[tableName.str.contains('_sg_')]
out_tables_list = out_tables.to_list()

for name in out_tables_list:
    pd.read_sql("DROP TABLE P_SMO_INP_T.{}".format(name), con=connection)

Can you please help me figure out what's my mistake? Thank you in advance!

LE: See below the full output I am receiving:

TypeError                                 Traceback (most recent call last)
<ipython-input-46-1e7a629dac7d> in <module>
      1 for name in out_tables_list:
----> 2     pd.read_sql("DROP TABLE P_SMO_INP_T.{}".format(name), con=connection)

c:\users\sgulunga\appdata\local\programs\python\python38-32\lib\site-packages\pandas\io\sql.py in read_sql(sql, con, index_col, coerce_float, params, parse_dates, columns, chunksize)
    481 
    482     if isinstance(pandas_sql, SQLiteDatabase):
--> 483         return pandas_sql.read_query(
    484             sql,
    485             index_col=index_col,

c:\users\sgulunga\appdata\local\programs\python\python38-32\lib\site-packages\pandas\io\sql.py in read_query(self, sql, index_col, coerce_float, params, parse_dates, chunksize)
   1726         args = _convert_params(sql, params)
   1727         cursor = self.execute(*args)
-> 1728         columns = [col_desc[0] for col_desc in cursor.description]
   1729 
   1730         if chunksize is not None:

TypeError: 'NoneType' object is not iterable

Answer 1

A DROP query returns nothing, so None , and so pandas can't iterate on that to build a dataframe.

See How do I drop a table in SQLAlchemy when I don't have a table object?

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Note that when debugging be careful about the line raising the error, you said "although the list is not empty" but the line raising the error doesn't use the list