import numpy as np
from numpy.lib.format import open_memmap
from pathlib import Path

path = Path("sensor-readings.npy")

mapped = open_memmap(path, mode="w+", dtype=np.float32, shape=(3, 4))
mapped[:] = np.arange(12, dtype=np.float32).reshape(3, 4)
mapped[-1, -1] = 99
mapped.flush()

readonly = np.load(path, mmap_mode="r")

print("mapped type:", type(mapped).__name__)
print("readonly type:", type(readonly).__name__)
print("mapped shape:", mapped.shape)
print("mapped dtype:", mapped.dtype)
print("readonly writeable:", readonly.flags.writeable)
print("last row:", readonly[-1].tolist())
print("saved value:", float(np.load(path)[-1, -1]))