Tuple usage

For example, we have a collection of e-mail addresses (haystack), but also to maintain a small collection of e-mail address (needles), and then find the needles in the number of address also appears in the heystack years. With a collection operation, we only need one line of code on it

The number of needles in the haystack elements appear, the two types of variables are set

found = len(needles & haystack)

found = 0
for n in needles:
    if n in haystack:
        found += 1