File not found error using subprocess in python

Question

I am using python 3.6.9 on my ubuntu 18.04LTS install and trying to use the subprocess library to call a compiled C++ function. The function takes no arguments so I would figure this should work:

subprocess.Popen(["ais"], stdout=subprocess.PIPE)

but doing so returns

>>> Popen(["ais"])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.6/subprocess.py", line 729, in __init__
    restore_signals, start_new_session)
  File "/usr/lib/python3.6/subprocess.py", line 1364, in _execute_child
    raise child_exception_type(errno_num, err_msg, err_filename)
FileNotFoundError: [Errno 2] No such file or directory: 'ais': 'ais'

This is a little confusing to me given that calling os.listdir() from the same directory returns:

>>> print(os.listdir())
['COM6 ARPA_A.txt', 'dataStream.py', 'arpa.cpp', 'arpa', 'COM7 AIS.txt', 'ais.cpp', 'ais']

Unless cwd (or .) is in the current PATH you wouldn't have been able to type out ais in the shell and have your program execute, you would have had to type out ./ais. So do the same thing and run Popen(["./ais"]) instead. This of course assumes ais has the executable bit set. — metatoaster
– metatoaster, Commented Jul 6, 2020 at 14:34
Oh wow I thought for sure I had tried that, but yes that was it. Thank you — Morten Nissov
– Morten Nissov, Commented Jul 6, 2020 at 14:34

Jazib Dawre · Accepted Answer · 2020-07-06 14:35:00Z

1

For executing a file you have to use './filename'

from reading your above comment, you have to give executable permission to the file which can be done as:

chmod +x ais

Reason for which is well explained here: https://unix.stackexchange.com/a/4432/399463

answered Jul 6, 2020 at 14:35

Jazib Dawre

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