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I have an algorithm that is written in C++ that outputs a cout debug statement to the terminal window and I would like to figure out how to read that printout with python without it being piped/written to a file or to return a value.

Python organizes how each of the individual C++ algorithms are called while the data is kept on the heap and not onto disk. Below is an example of the a situation that is of similar output,

+-------------- terminal window-----------------+

(c++)runNewAlgo: Debug printouts on

(c++)runNewAlgo: closing pipes and exiting 

(c++)runNewAlgo: There are 5 objects of interest found

( PYTHON LINE READS THE PRINT OUT STATEMENT)

(python)main.py: Starting the next processing node, calling algorithm

(c++)newProcessNode: Node does work

+---------------------------------------------------+

Say the line of interest is "there are 5 objects of interest" and the code will be inserted before the python call. I've tried to use sys.stdout and subprocess.Popen() but I'm struggling here.

M-Chen-3
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kylernstlol
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  • I don't understand. Your question is about Python, but you tag as C++. Are you mixing the languages? If not, only tag the language you will be using. – Thomas Matthews Dec 28 '20 at 19:27
  • Will you start the C++ algorithm from within the python script or externally? Would piping the output to python work for you? – Marc Dec 28 '20 at 19:27
  • @ThomasMatthews I was the one that edited in the C++ tag. I did so because the OP wants to read the printout of a C++ program with Python, so therefore he is kind of mixing the languages. Did I do so incorrectly? – M-Chen-3 Dec 28 '20 at 19:29
  • the languages are mixed in the API that is being used. The C++ algorithm is started from within the python script. Piping may be of use but this is run remotely which may cause a memory backup if not managed correctly. – kylernstlol Dec 28 '20 at 19:34

2 Answers2

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Your easiest path would probably be to invoke your C++ program from inside your Python script.

More details here: How to call an external program in python and retrieve the output and return code?

Meldroc
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You can use stdout from the returned process and read it line-by-line. The key is to pass stdout=subprocess.PIPE so that the output is sent to a pipe instead of being printed to your terminal (via sys.stdout).

Since you're printing human-readable text from your C++ program, you can also pass encoding='utf-8' as well to automatically decode each line using utf-8 encoding; otherwise, raw bytes will be returned.

import subprocess

proc = subprocess.Popen(['/path/to/your/c++/program'],
                        stdout=subprocess.PIPE, encoding='utf-8')
for line in proc.stdout:
  do_something_with(line)
  print(line, end='') # if you also want to see each line printed
Brandon
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