Running an outside program (executable) in Python?


I just started working on Python, and I have been trying to run an outside executable from Python.

I have an executable for a program written in Fortran. Let’s say the name for the executable is flow.exe. And my executable is located in C:\Documents and Settings\flow_model. I tried both os.system and popen commands, but so far I couldn't make it work. The following code seems like it opens the command window, but it wouldn't execute the model.

# Import system modules
import sys, string, os, arcgisscripting
os.system("C:/Documents and Settings/flow_model/flow.exe")

How can I fix this?

6/3/2018 3:13:43 PM

Accepted Answer

Those whitespaces can really be a bother:-(. Try os.chdir('C:/Documents\ and\ Settings/') followed by relative paths for os.system, subprocess methods, or whatever...

If best-effort attempts to bypass the whitespaces-in-path hurdle keep failing, then my next best suggestion is to avoid having blanks in your crucial paths. Couldn't you make a blanks-less directory, copy the crucial .exe file there, and try that? Are those havoc-wrecking space absolutely essential to your well-being...?

11/28/2009 6:08:35 AM

If using Python 2.7 or higher (especially prior to Python 3.5) you can use the following:

import subprocess
  •, *, stdin=None, stdout=None, stderr=None, shell=False) Runs the command described by args. Waits for command to complete, then returns the returncode attribute.
  • subprocess.check_call(args, *, stdin=None, stdout=None, stderr=None, shell=False) Runs command with arguments. Waits for command to complete. If the return code was zero then returns, otherwise raises CalledProcessError. The CalledProcessError object will have the return code in the returncode attribute

Example: subprocess.check_call([r"C:\pathToYourProgram\yourProgram.exe", "your", "arguments", "comma", "separated"])

In regular Python strings, the \U character combination signals a extended Unicode code point escape.

Here is the link to the documentation:

For Python 3.5+ you can now use run() in many cases:


The simplest way is:

import os
os.startfile("C:\Documents and Settings\flow_model\flow.exe")

It works; I tried it.


I'd try inserting an 'r' in front of your path if I were you, to indicate that it's a raw string - and then you won't have to use forward slashes. For example:

os.system(r"C:\Documents and Settings\flow_model\flow.exe")

Your usage is correct. I bet that your external program, flow.exe, needs to be executed in its directory, because it accesses some external files stored there.

So you might try:

import sys, string, os, arcgisscripting
os.chdir('c:\\documents and settings\\flow_model')
os.system('"C:\\Documents and Settings\\flow_model\\flow.exe"')

(Beware of the double quotes inside the single quotes...)


Use subprocess, it is a smaller module so it runs the .exe quicker.

import subprocess
subprocess.Popen([r"U:\Year 8\kerbal space program\KSP.exe"])

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