python - udpclient error

[fico14]

If I run "python3 udpclient.py freq 101000000" I get the following error:

Traceback (most recent call last):
File "/home/fico/Desktop/Projekt/rtl_fm_modified/rtl-sdr/udpclient.py", line 48, in
s.send(buf)
TypeError: a bytes-like object is required, not 'str'

I have tried to encode buf like this:
s.send(buf.encode())

and the program doesn't crash but nothing happens to the frequency.