list. append with negative integer?

Question

why does this code keep pushing 7 outside are they different elements?

light= [[1]]

def add_value():
light.append ([light[-1],7])
print(light)

add_value()
add_value()
add_value()

-------------------------------------------
output

[[1], [[1], 7]]
[[1], [[1], 7], [[[1], 7], 7]]
[[1], [[1], 7], [[[1], 7], 7], [[[[1], 7], 7], 7]]

Answer 1

Thanks