How to diagnose this, fails on 3.6.3, works on 3.5.2?

[Peter Otten]

Chris Green wrote:

> I have a fairly simple little python program to automate starting an
> editor on a wiki page.  It works fine on the system where I wrote it
> (xubuntu 16.04, python 3 version 3.5.2) but it comes up with the
> following error on a newer system (xubuntu 17.10, python 3 version
> 3.6.3).
> 
> Here is the error:-
> 
>     chris$ no
>     Traceback (most recent call last):
>       File "/home/chris/bin/no", line 59, in <module>
>         os.execvp("vi", ("", monthFile,))
>       File "/usr/lib/python3.6/os.py", line 559, in execvp
>         _execvpe(file, args)
>       File "/usr/lib/python3.6/os.py", line 594, in _execvpe
>         exec_func(fullname, *argrest)
>     ValueError: execv() arg 2 first element cannot be empty
> 
> Has execvp() become stricter in 3.6.3 or what?

Yes; the relevant issue on the bug tracker seems to be

https://bugs.python.org/issue28732

> ... and here is the program:-

[snip]

A smaller demo is

$ cat demo.py
import os
os.execvp("ls", ("",))
$ python3.5 demo.py 
demo.py
$ python3.6 demo.py 
Traceback (most recent call last):
  File "demo.py", line 2, in <module>
    os.execvp("ls", ("",))
  File "/usr/local/lib/python3.6/os.py", line 559, in execvp
    _execvpe(file, args)
  File "/usr/local/lib/python3.6/os.py", line 594, in _execvpe
    exec_func(fullname, *argrest)
ValueError: execv() arg 2 first element cannot be empty