Python MySQLdb test for select count(*) = zero

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I use SELECT COUNT(*) FROM db WHERE <expression> to see if a set of records is null. So:

>>> cnt = c.fetchone()
>>> print cnt
(0L,)

My question is: how do you test for this condition?
I have a number of other ways to accomplish this. Is something like the following possible?

if cnt==(0L,):
    # do something

fetchone returns a row, which is a sequence of columns.
If you want to get the first value in a sequence, you use [0].

You could instead compare the row to (0,), as you're suggesting. But as far as I know neither the general DB-API nor the specific MySQLdb library guarantee what kind of sequence a row is; it could be a list, or a custom sequence class. So, relying on the fact that it's a tuple is probably not a good idea. And, since it's just as easy to not do so, why not be safe and portable?

So:

count_row = c.fetchone()
count = count_row[0]
if count == 0:
    do_something()

Or, putting it together in one line:

if c.fetchone()[0] == 0:
    do_something()

source： stackoverflow