using python join to join first element of each list

Question

I'd like to do this:

for qb in qb_data:
    qb_in += "'" + qb[0] + "'" + ","

using a join. Obviously the problem is that join just concatenates each member of the list. But here I have a list of lists and only need to join the first element of each list.

Answer 1

",".join("'%s'" % qb[0] for qb in qb_data)

You can still selectively pick out stuff in your generator expression/list comprehension, of course!

For example:

>>> qb_data = [['1', '2'], ['3', '4'], ['5', '6'], ['7', '8', '9']]
>>> ",".join("'%s'" % qb[0] for qb in qb_data)
"'1','3','5','7'"