About mysql cursor and iterator

Imagine I have a mysql cursor 开发者_运维问答and data read. The amount of data might be very big that I want to deal with one line each time.

An easy and straight forward way might be like this:

while True:
    row = cursor.fetchone()
    if not row: break
    .....

But this doesn't look good, so I wonder whether this way works as imagined:

for row in iter(cursor.fetchall())

The thing I want to know is: if I use the iter(cursor.fetchall()) way, does it fetch all the data first or it just fetch one row at a time?

The MySQLdb cursor class implements the iterator protocol, so you can simply do this:

cursor.execute(sql)
for row in cursor:
    print row
    ...

Relevant code from MySQLdb.cursors.BaseCursor:

def __iter__(self):
    return iter(self.fetchone, None)