numpy array index offset

index_offset.py

import numpy as np

def index_offset(a):
    if a.base is None:
        ravel_index = 0
        shape = a.shape
    else:
        byte_offset = np.byte_bounds(a)[0] - np.byte_bounds(a.base)[0]
        ravel_index = byte_offset // a.dtype.itemsize
        shape = a.base.shape
    return np.unravel_index(ravel_index, shape)


if __name__ == '__main__':
    a = np.ones((50, 60, 100), dtype=np.uint64)
    b = a[21:46, 33:61, 78:98]

    index_offset(a)
    # (0, 0, 0)

    index_offset(b)
    # (21, 33, 78)