# Data:
 list = [-1, 1, 2, 3, -1, 4, 5, 6, -1]

# == Determine bondaries ===

minus = []

# iterate over list
for l in range(len(list)):
    if list[l] == -1:
        minus.append(l)

# add a dividing point to end if no -1 present
if list[len(list)-1] != -1:
    minus.append(len(list))


# == Exract segments ===

segments = []

# set boundary manually to one earlier if we're not starting with a -1
if list[0] != -1:
    last = -1

last = 0
for m in minus:
    if not last == m:
        segments.append(list[last:m])
    last = m + 1

for segment in segments:
    print(segment)