class Unit:
    x = 0
    y = 0
    range = 0

    def __init__(self, x, y, range):
        self.x = x
        self.y = y
        self.range = range

test1 = Unit(10, 10, 5)
test2 = Unit(20, 20, 5)
test3 = Unit(30, 30, 7)

test_list = [test1, test2, test3]

test_list_attr = [test1.y, test2.y, test3.y]

test_list_attr = [i.y for i in test_list]

from operator import attrgetter

test_list_attr = list(map(attrgetter('y'), test_list))