使用Sqlite3和python运行查询时'NoneType'对象不可迭代错误

Question

I wanted to create a table in a database on Jupyter Notebook using Python and sqlite3. To avoid the table already exists error, I used the following code:

    q1 = '''
    CREATE TABLE IF NOT EXISTS person (
        person_id TEXT PRIMARY KEY,
        first_name TEXT,
        last_name TEXT
    );
'''
run_query(q1)

However I received this error and I can't get rid of it.

TypeErrorTraceback (most recent call last)
<ipython-input-25-948d42611e56> in <module>()
      7 
      8 '''
----> 9 run_query(q1)

<ipython-input-13-67c680d27fbe> in run_query(q)
      3 def run_query(q):
      4     with sqlite3.connect(db) as conn:
----> 5         return pd.read_sql(q,conn)
      6 
      7 def run_command(c):

/dataquest/system/env/python3/lib/python3.4/site-packages/pandas/io/sql.py in read_sql(sql, con, index_col, coerce_float, params, parse_dates, columns, chunksize)
    398             sql, index_col=index_col, params=params,
    399             coerce_float=coerce_float, parse_dates=parse_dates,
--> 400             chunksize=chunksize)
    401 
    402     try:

/dataquest/system/env/python3/lib/python3.4/site-packages/pandas/io/sql.py in read_query(self, sql, index_col, coerce_float, params, parse_dates, chunksize)
   1443         args = _convert_params(sql, params)
   1444         cursor = self.execute(*args)
-> 1445         columns = [col_desc[0] for col_desc in cursor.description]
   1446 
   1447         if chunksize is not None:

TypeError: 'NoneType' object is not iterable

The table was created when I checked and the columns are there.

Any help would be greatly appreciated.

Answer 1

run_query() uses read_sql() which was created to read rows from database, not to create tables or insert rows. read_sql() expects that query will get rows from database and it try to iterate these rows but CREATE returns None - and you get 'NoneType' object is not iterable

You should rather use directly execute(query) - ie.

 with sqlite3.connect(db) as conn:
      conn.execute(q1)