Python 3: how to send random number of bytes over the COM(serial) port

Question

I wrote a Python script in which I can send fixed bytes through a COM port.

ser.write(bytes('0123456789',encoding='ascii'))

I want to parameterize the number of bytes that the script can send.

Can anyone please suggest me how I can do this?

Thanks.

Have you tried creating a random-length bytes value and passing it to your ser.write() function? If not, what have you tried? — DisappointedByUnaccountableMod
– DisappointedByUnaccountableMod, Commented Aug 19, 2015 at 22:51
Do you mean you want to restrict the number of bytes sent to a specific value? Suppose that ser.write has another parameter numBytes. What happens if NumBytes is 6 in your example? What if numBytes is 16? — saulspatz
– saulspatz, Commented Aug 19, 2015 at 23:57

mhawke · Accepted Answer · 2015-08-20 01:59:06Z

By "random" I think you mean "arbitrary", i.e. how to send an arbitrary number of bytes...

You can generate a sequence of repeating digits like this:

>>> ''.join([str(i%10) for i in range(21)]) '012345678901234567890'

The number of bytes required can be passed to the script as a command line argument. Its value will be available in the sys.argv[] list.

import sys import serial try: num_bytes = int(sys.argv[1]) except (IndexError, ValueError): sys.stderr.write('Usage: {} num-bytes\n'.format(sys.argv[0])) sys.exit(1) ser = serial.Serial() # set up your serial port digits = ''.join(str(i%10) for i in range(num_bytes)) num_written = ser.write(bytes(digits, 'ascii'))

Invoke the command like this:

$ python3 send_bytes.py 42

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