Large list, find all minima of list (python)

Question

Given a large list of fluctuating values, how do you determine all local min values? Not using numpy. Local minimum means all values in a list that are the troughs

Answer 1

def local_min(ys):
    return [y for i, y in enumerate(ys)
            if ((i == 0) or (ys[i - 1] >= y))
            and ((i == len(ys) - 1) or (y < ys[i+1]))]


>>> local_min([23, 8, -7, 57, 87, 6])
[-7, 6]
>>> local_min([23, 6, 6, 6, 42])
[6]
>>> local_min([6, 6, 4])
[4]