def numberfunction(s):
    if s == "":
        return 0
    if s < 0:
        return -1
    if s > 0:
        return s

from functools import partial
a, x = [[1, 2, 3, ""], [-1, 1, -1, 1], [2, -2, -2, 2]], partial(map, numberfunction)
print map(x, a)