Error saying ValueError Invalid file object io BufferedReader name 9

Question

I am trying to get a file name and pass it to a command using popen. Then I want to print the output. This is my code:

filePath = tkinter.filedialog.askopenfilename(filetypes=[("All files", "*.*")])

fileNameStringForm = (basename(filePath ))
fileNameByteForm = fileNameStringForm.encode(encoding='utf-8')

process = subprocess.Popen(['gagner','-arg1'], shell = True, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
process .communicate(fileNameByteForm )

stdout, stderr = process .communicate()  <<------ERROR POINTS TO THIS LINE

stringOutput = stdout.decode('urf-8')
print(stringOutput)

I am getting the following error:

ValueError: Invalid file object: <_io.BufferedReader name=9>

Answer 1

Once you've executed the following command, your subprocess has finished and the pipes have been closed and hence the second call will fail

process.communicate(fileNameByteForm)

your subprocess has finished and the pipes have been closed. The second call will then fail as a result.

What you want to do instead is

stdout, stderr = process.communicate(input_data)

This will pipe your input data into the subprocess and read stdout and stderr.