I'm looking at the I2C.writeto() method and I see it returns the number of ACKs received. So out of curiosity, I put some print statements in my code.

def measure(self):
    acks = self._i2c.writeto(self._i2c_addr, BH1750.POWER_ON.to_bytes())
    print("Power On ACKs:", acks)
    acks = self._i2c.writeto(self._i2c_addr, BH1750.ONE_TIME_HRES.to_bytes())
    print("Measure One Time ACKs:", acks)

When I run it, I see this:

Power On ACKs: 1
Measure One Time ACKs: 1

However, in the device datasheet, I see this example exchange:

ST | Address | R/W 0 | Ack | Opecode | Ack | SP

It seems like there should be two ACKs: one to acknowledge the receipt of the address, and another to acknowledge the receipt of the command. At least that's the way the datasheet makes it look. But I only see one ACK returned from I2C.writeto().

Is the ACK for the address implied and not counted in the total?

I'm thinking that a check of the number of ACKs received would be useful in determining if the device indeed got the command. But I'm left wondering how many ACKs there should be.