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 using subpocess for both reading and writing simultaneously
#11
(May-30-2018, 08:43 PM)killerrex Wrote: 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
(May-30-2018, 08:43 PM)killerrex Wrote: 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
Test everything in a Python shell (iPython, Azure Notebook, etc.)
  • Someone gave you an advice you liked? Test it - maybe the advice was actually bad.
  • Someone gave you an advice you think is bad? Test it before arguing - maybe it was good.
  • You posted a claim that something you did not test works? Be prepared to eat your hat.
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#12
I am so used to use the './' that I do not even notice I was using it...

In unix-like systems the current directory is never in the search path except if you add it to your environment with PATH="${PATH}:." (please, never, ever do this) so you need to add the './' to the script name.
In windows the default behaviour was like having the PATH=".:${PATH}" declared so local versions of program and dll have priority over the system ones. I do not have now any windows machine to test if subprocess.Popen also follows this rule or not.
I guess that Popen just let the OS to look for the executable and in Windows it shall work without the './' in the command, but in any case this is something to check for scripts that shall work in different SO.
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