using subpocess for both reading and writing simultaneously

[volcano63]

I try not to use the shell=True mode... some bad experiences with the shell expansions.

I was just explaining why it could not work - not urging to use it

But for a python script that is in the same folder works in both ways as long as you set it executable.

OK, I set it executable and added shebang line - still need to add path - even if it is just ./

Output:
In [4]: subprocess.Popen(['cpt.py'])
---------------------------------------------------------------------------
FileNotFoundError                         Traceback (most recent call last)
<ipython-input-4-294e3396b106> in <module>()
----> 1 subprocess.Popen(['cpt.py'])

/usr/lib/python3.6/subprocess.py in __init__(self, args, bufsize, executable, stdin, stdout, stderr, preexec_fn, close_fds, shell, cwd, env, universal_newlines, startupinfo, creationflags, restore_signals, start_new_session, pass_fds, encoding, errors)
    707                                 c2pread, c2pwrite,
    708                                 errread, errwrite,
--> 709                                 restore_signals, start_new_session)
    710         except:
    711             # Cleanup if the child failed starting.

/usr/lib/python3.6/subprocess.py in _execute_child(self, args, executable, preexec_fn, close_fds, pass_fds, cwd, env, startupinfo, creationflags, shell, p2cread, p2cwrite, c2pread, c2pwrite, errread, errwrite, restore_signals, start_new_session)
   1342                         if errno_num == errno.ENOENT:
   1343                             err_msg += ': ' + repr(err_filename)
-> 1344                     raise child_exception_type(errno_num, err_msg, err_filename)
   1345                 raise child_exception_type(err_msg)
   1346 

FileNotFoundError: [Errno 2] No such file or directory: 'cpt.py': 'cpt.py'

In [5]: subprocess.Popen(['./cpt.py'])
Out[5]: <subprocess.Popen at 0x7fcc683ccdd8>

As you can see, without specifying path to the script, it is still not found - not by subprocess.Popen but rather by the opened sub-shell