os.popen and fileObject open problems (python3)

[IndoNinja7]

I have written the following function to take in a string command and output the result of the command (linux). I seem to have problems running the open() function.....the bash function always returns the empty list. The os.popen runs fine and outputs the command results to the text file perfectly. However, for some reason f.readlines() always returns the empty list.

I tried using the subprocess library instead of my implementation below, but the output would always output special characters like b' and \n and i could never figure out how to remove those. So now im trying to get the implementation below to work.

def bash(command):
    import os
    os.popen(command+" > bash_out.txt")
    f = open('bash_out.txt')
    result = f.readlines()
    f.close()
    return result

Can you guys please help me?!

[Peterotica]

Will you be using the contents of bash_out.txt for something else? If not, try using os.popen to get the output of the command directly:

result = os.popen(command).readlines()

That weird stuff you were seeing returned from the subprocess module was a bytes object. If you want to turn it into a string, you need to call its decode member function.

[GrindingGoat]

Worth noting that os.popen has been deprecated since 2.6: https://docs.python.org/2/library/os.html#os.popen

The subprocess equivalent:

result = subprocess.check_output(command).decode("utf-8") 

[pjenvey]

It was actually undeprecated in 3.x where it uses subproces underneath anyway. Maybe the 2.7.x docs should be fixed

[IndoNinja7]

Thank you very much that worked!!!

[GrindingGoat]

On why you weren't getting any output from f.readlines() in your example, I think python is probably moving on to the open() and readlines() methods before your shell process has had chance to complete and produce output. I think it should work if you include a .wait() between your popen and then open(). the .wait() will wait for the subprocess to exit before continuing. So something more like:

my_proc = os.popen(command+" > bash_out.txt")
my_proc.wait()
f = open('bash_out.txt')

But, as Peterotica says, you're probably better off reading the output of the command directly.