How to run several times the same program with different inputs via Python script?

Question

I need to run a simple C program several time, each one with different input string (let's say AAAAA... increasing size, until I get "TRUE" as output). e.g.

./program A # output FALSE
./program AA # output FALSE
./program AAA # output FALSE
./program AAAA # output FALSE
./program AAAAA # output FALSE
./program AAAAAA # output FALSE
./program AAAAAAA  # output TRUE

in C I would simply use a while loop. I know in python there is the while loop as well.

So the python program would be:

strlen = 0
while TRUE
 strlen++
 <run ./**C program** "A"*strlen > 
 if (<program_output> = TRUE)
   break

Given that I can make the .py script executable by writing

#! /usr/bin/env python

and

 chmod +x file.py

What should I do to make this work?

Thanks in advance

I know, the syntax is not the right one. it's just an example — dragonmnl
– dragonmnl, Commented Mar 5, 2014 at 17:33

Valentin Lorentz · Accepted Answer · 2014-03-05 17:33:27Z

4

You can use subprocess.check_output:

import subprocess
strlen = 0
while True:
    strlen += 1
    if subprocess.check_output(['./program', 'A'*strlen]) == 'TRUE':
        break

answered Mar 5, 2014 at 17:33

Valentin Lorentz

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3 Comments

dragonmnl Over a year ago

I tried the code. It seems to work.. but after 1 loop only it gets stuck. I tried to place print(strlen) after strlen +=1 and indeed it prints 1 only and nothing more (nor the program exits)

dragonmnl Over a year ago

actually it doesn't. he program (./program) after every execution requires a user interrupt (ctrl+C) to stop. And obviously if I do it, the program ./program exists, as well as the .py program. is there any one to make ./program exit, but the .py continue?

Valentin Lorentz Over a year ago

You can set a timeout argument to check_output (see the doc linked above). A cleaner way would be to use subprocess.Popen directly (check_output is a wrapper), read the four first characters from the process' stdout, and then kill it.

Friendly King · Accepted Answer · 2014-03-05 18:55:07Z

2

You could try something like this (see docs):

import subprocess

args = ""
while True:
     args += "A"
     result = subprocess.call(["./program", "{args}".format(args=args)])
     if result == 'TRUE':
         break

The subprocess module is preferred to the os.popen command, since it has been "deprecated since version 2.6." See the os documentation.

edited Mar 5, 2014 at 18:55

answered Mar 5, 2014 at 17:32

Friendly King

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3 Comments

dragonmnl Over a year ago

program is not a .py script, but a C program

dragonmnl Over a year ago

the code works. why do you use "args"? However, the program (./program) after every execution requires a user interrupt (ctrl+C) to stop. And obviously if I do it, the program ./program exists, as well as the .py program. is there any one to make ./program exit, but the .py continue?

Friendly King Over a year ago

I was using 'args' to refer to the command-line arguments you would be passing in, had you simply ran your c file from command line. You could call that variable whatever you want. And you might be able to do a result.kill() with the revised subprocess.Popen(...)

Ashoka Lella · Accepted Answer · 2014-03-05 17:31:27Z

1

file.py

import os

count=10
input="A"
for i in range(0, count):
    input_args=input_args+input_args
    os.popen("./program "+input_args)

running file.py would execute ./program 10 times with increasing A input

answered Mar 5, 2014 at 17:31

Ashoka Lella

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2 Comments

dragonmnl Over a year ago

program is not a .py script, but a C program

Ashoka Lella Over a year ago

@dragonmnl made changes to run program as executable

Sudeep Juvekar · Accepted Answer · 2014-03-05 17:34:23Z

1

Use commands. Here is the documentation http://docs.python.org/2/library/commands.html

commands.getstatusoutput returns a stdout output from your C program. So, if your program prints something, use that. (In fact, it returns a tuple (0, out) for stdout).
commands.getstatus returns boolean status from program which you can use as well.

So, assuming you are using stdout to capture the ./program output, the entire modified program looks like

import commands

while TRUE:
  strlen += 1
  output = commands.getstatusoutput("./program " + "A"*strlen)
  outstatus = output[1]
  if output == "true":
     break

I would experiment with getstatus to see if I can read values returned by program.

Edit: Didn't notice that commands is deprecated since 2.6 Please use subprocess as shown in other response.

answered Mar 5, 2014 at 17:34

Sudeep Juvekar

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2 Comments

Martijn Pieters Over a year ago

Don't use commands. Use the subprocess module instead. The big fat warning at the top of the documentation for commands tells you: Deprecated since version 2.6.

Sudeep Juvekar Over a year ago

Oops.. Didn't notice the deprecated part. I used it sometime back, not recently

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