First common element from two lists

Question

x = [8,2,3,4,5]
y = [6,3,7,2,1]

How to find out the first common element in two lists (in this case, \"2\") in a concise and elegant way? Any list

Answer 1

One liner, using next to take the first item from a generator:

x = [8,2,3,4,5]
y = [6,3,7,2,1]

first = next((a for a in x if a in y), None)

Or more efficiently since set.__contains__ is faster than list.__contains__:

set_y = set(y)
first = next((a for a in x if a in set_y), None)

Or more efficiently but still in one line (don't do this):

first = next((lambda set_y: a for a in x if a in set_y)(set(y)), None)