How do I sort a list with positives coming before negatives with values sorted respectively?

You could just use a regular sort, and then bisect the list at 0:

>>> lst
[1, -2, 10, -12, -4, -5, 9, 2]
>>> from bisect import bisect
>>> lst.sort()
>>> i = bisect(lst, 0)  # use `bisect_left` instead if you want zeroes first
>>> lst[i:] + lst[:i]
[1, 2, 9, 10, -12, -5, -4, -2]

The last line here takes advantage of a slice invariant lst == lst[:n] + lst[n:]

Another option would be to use a tuple as a sort key, and rely on lexicographical ordering of tuples:

>>> sorted(lst, key=lambda x: (x<0, x))  # use <= instead if you want zeroes last
[1, 2, 9, 10, -12, -5, -4, -2]