Windows can't find the file on subprocess.call()

Question

When the command is a shell built-in, add a shell=True to the call.

E.g. for dir you would type:

import subprocess
subprocess.call('dir', shell=True)

To quote from the documentation:

The only time you need to specify shell=True on Windows is when the command you wish to execute is built into the shell (e.g. dir or copy). You do not need shell=True to run a batch file or console-based executable.

On Windows, I believe the subprocess module doesn't look in the PATH unless you pass shell=True because it use CreateProcess() behind the scenes. However, shell=True can be a security risk if you're passing arguments that may come from outside your program. To make subprocess nonetheless able to find the correct executable, you can use shutil.which. Suppose the executable in your PATH is named frob:

subprocess.call([shutil.which('frob'), arg1, arg2])

(This works on Python 3.3 and above.)

On Windows you have to call through cmd.exe. As Apalala mentioned, Windows commands are implemented in cmd.exe not as separate executables.

e.g.

subprocess.call(['cmd', '/c', 'dir'])

/c tells cmd to run the follow command

This is safer than using shell=True, which allows shell injections.

If you are using powershell, then in it will be subprocess.call(['powershell','-command','dir']). Powershell supports a large portion of POSIX commands

After much head scratching, I discovered that running a file that is located in C:\Windows\System32\ while running a 32bit version of python on a 64bit machine is a potential issue, due to Windows trying to out-smart the process, and redirect calls to C:\Windows\System32 to C:\Windows\SysWOW64.

I found an example of how to fix this here: http://code.activestate.com/recipes/578035-disable-file-system-redirector/