polygon = [[1,1], [2,5], [6,8], [10,9]]

if len(polygon) < 3:
    print "not a valid polygon"
elif len(polygon) == 3:
    print "the polygon is a triangle"
elif len(polygon) == 4:
    print "the polygon has four sides (and could be a square)"
else:
    print "it's a more complex polygon"