Find the minimum dtype required to represent the elements of an integer array.

min_dtype.py

import numpy as np

dtype_range = [(np.bool, (False, True)),
               (np.bool8, (False, True)),
               (np.uint8, (0, 255)),
               (np.int8, (-128, 127)),
               (np.uint16, (0, 65535)),
               (np.int16, (-32768, 32767)),
               (np.uint32, (0, 4294967295)),
               (np.int32, (-2147483648, 2147483647)),
               (np.uint64, (0, 18446744073709551615)),
               (np.int64, (-9223372036854775808, 9223372036854775807))]

def min_typecode(a):
    """Find the minimum type code needed to represent the integers in `a`.

    """
    a = np.asarray(a)

    if not np.issubdtype(a.dtype, np.integer):
        raise ValueError("Can only handle integer arrays.")

    a_min, a_max = a.min(), a.max()

    for t, (t_min, t_max) in dtype_range:
        if np.all(a_min >= t_min) and np.all(a_max <= t_max):
            return t
    else:
        raise ValueError("Could not find suitable dtype.")


if __name__ == "__main__":
    print "[0, -1] -> ", min_typecode([0, -1])
    print "[0, 256] -> ", min_typecode([0, 256])
    print "[-1, 256] -> ", min_typecode([-1, 256])