discrepancy in results during conversion from int to bytes and vice versa provides in python3

Question

I am using python3.4 in a venv.

I am writing a script for a sensor where, after reading a configuration file I need to send an int to the serial port in bytearray

a snippet of the class function is:

def set_sampling(self, type, sampling_us):
        conf_buffer = bytearray([0xfe, 0x06])
        if type not in self.sensor_ids:
            print('Sensor not identified')
        else:
            conf_buffer.append(self.sensor_ids[type])
            conf_buffer.append(0x02)
            if (sampling_us > 0):
                print(sampling_us)
                sampling_bytes = (sampling_us).to_bytes(4, 'little')
                conf_buffer += sampling_bytes
            self.send_frame(conf_buffer)
            self.enable(type)

the frame structure is 0xf6 0x06 sensor_id 0x02 sampling_us where sampling_us should be in little-endian format

I have currently sampling_us as 1000000 (equals to 1 second)

When I perform the following in the interpreter:

>>> (1000000).to_bytes(4, 'little')

the result provided is:

>>> b'@B\x0f\x00'

however I cross-checked with a script for the sensor where the bytes for 1000000 is actually b'\x40\x42\x0f\x00'

I reversed the check by performing:

 >>> int.from_bytes(b'\x40\x42\x0f\x00', 'little')
 >>> 1000000

the correct bytes are in fact b'\x40\x42\x0f\x00' as the sensor does not respond if the bytearray sent to it is b'@B\x0f\x00'

Why am I getting a discrepancy here? what is it I am doing wrong here?

score 3 · Accepted Answer · answered May 22 '19 at 09:57

If you do this

>>> b'\x40\x42\x0f\x00' == b'@B\x0f\x00'
True

you will see there is no discrepancy, you are just looking at two different representations of the same bytestring. In b'...' notation, Python's default presentation is that any printable ascii character is shown as that character and not as an \x escape.

discrepancy in results during conversion from int to bytes and vice versa provides in python3

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