While fixing #8391, I realized that subprocess doesn't support bytes program name if it's not an absolute path:
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$ ./python
>>> import subprocess
>>> subprocess.call([b'echo'])
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/home/SHARE/SVN/py3k/Lib/subprocess.py", line 449, in call
return Popen(*popenargs, **kwargs).wait()
File "/home/SHARE/SVN/py3k/Lib/subprocess.py", line 681, in __init__
restore_signals, start_new_session)
File "/home/SHARE/SVN/py3k/Lib/subprocess.py", line 1116, in _execute_child
for exe in executable_list)
File "/home/SHARE/SVN/py3k/Lib/subprocess.py", line 1115, in <genexpr>
executable_list = tuple(fs_encode(exe)
File "/home/SHARE/SVN/py3k/Lib/subprocess.py", line 1114, in <genexpr>
for dir in path_list)
File "/home/SHARE/SVN/py3k/Lib/posixpath.py", line 75, in join
if b.startswith(sep):
TypeError: expected an object with the buffer interface
[62826 refs]
-------
I'm working on a patch.