fast list search?

[ramon aragues]

Hi,

I´ve got a list with more than 500,000 ints. Before inserting new ints, 
I have to check that it doesn´t exist already in the list.

Currently, I am doing the standard:

if new_int not in long_list:
	 long_list.append(new_int)


but it is extremely slow... is there a faster way of doing this in python?

Thanks a lot,

Ramon Aragues