Python mysql駆動mysql.connector fetchone(),fetchall(),fetchmany()

def fetchone(self):
    """Returns next row of a query result set

     Returns a tuple or None.
     """
    row = self._fetch_row()
     if row:
        if hasattr(self._connection, 'converter'):
             return self._connection.converter.row_to_python(
                row, self.description)
         return row
     return None

 def fetchmany(self, size=None):
 
         """
     Returns the next set of rows of a query result, returning a
     list of tuples. When no more rows are available, it returns an
   empty list.
    The number of rows returned can be specified using the size argument,
    which defaults to one
     """
    res = []
    cnt = (size or self.arraysize)
     while cnt > 0 and self._have_unread_result():
         cnt -= 1
        row = self.fetchone()
         if row:
             res.append(row)
     return res


 def fetchall(self):
     """
     Returns all rows of a query result set

     Returns a list of tuples.
     """
    if not self._have_unread_result():
        raise errors.InterfaceError("No result set to fetch from.")
    (rows, eof) = self._connection.get_rows()
    if self._nextrow[0]:
        rows.insert(0, self._nextrow[0])

    if hasattr(self._connection, 'converter'):
        row_to_python = self._connection.converter.row_to_python
        rows = [row_to_python(row, self.description) for row in rows]

    self._handle_eof(eof)
    rowcount = len(rows)
    if rowcount >= 0 and self._rowcount == -1:
        self._rowcount = 0
    self._rowcount += rowcount
    return rows

見える

cursor.fetchall()    [()]   []     fetchone
      ，        raise errors.InterfaceError("No result set to fetch from.")     mysql.connector fetcall()       
cursor.fetchmany(size=1) [()] ,  []   size       fetchone
cursor.fetchone()  ()   None

        MySQLdb       ，  MySQLdb fectchall()