[storm] Testing the existance of values quickly

[akira]

Hi

I would like to test to see if a user is in a table before joing other 
tables to get his profile

Given this result set:
myrows = store.find(User, User.username==u"Akira")

How do I quickly test if there are results in the resultset? One cannot 
do len(myrows) or myrows = []. I dont like doing things the long way and 
first trying to extracti the data(List comprehension, for loop) and 
testing for None.

thanks