Need to be updated to work with python 3.8

[NofelYaseen]

I am following the README here: https://github.com/p4lang/PI/tree/main/proto/ptf

I get the error

======================================================================
ERROR: l3_host_fwd.FwdTest
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/vagrant/PI/proto/ptf/base_test.py", line 668, in handle
    return f(*args, **kwargs)
  File "/home/vagrant/PI/proto/ptf/l3_host_fwd/test/l3_host_fwd.py", line 43, in runTest
    eg_port_str = stringify(eg_port, 2)
  File "/home/vagrant/PI/proto/ptf/base_test.py", line 69, in stringify
    decoded_s = s.decode("hex")
AttributeError: 'str' object has no attribute 'decode'

I am using the vm in
https://github.com/p4lang/tutorials/tree/master/vm-ubuntu-20.04

The vm uses python version 3.8. I am not sure which is expected for it work?

[antoninbas]

I don't know where this code comes from, but it doesn't seem to be from this repo:

decoded_s = s.decode("hex")

The code is as follows:

PI/proto/ptf/base_test.py

Lines 66 to 68 in 5a4c56e

	h = '%x' % n
	s = ('0'*(len(h) % 2) + h).zfill(length*2).decode('hex')
	return s

However, this code is indeed invalid in Python3.
If someone wants to update the code and validate it with a recent version of Python, a PR would be very welcome.

[rst0git]

I have opened a pull request to update the code (#600). The update is straightforward because stringify() implements the equivalent functionality of int.to_bytes in Python 3.