Python Which/Where - Find executable

find_executable.py

#!/usr/bin/env python

# https://gist.github.com/4368898
# Public domain code by anatoly techtonik <techtonik@gmail.com>
# AKA Linux `which` and Windows `where`

# For Python 3 you probably want
# https://docs.python.org/dev/library/shutil.html#shutil.which

import os
import sys

def find_executable(executable, path=None):
    """Find if 'executable' can be run. Looks for it in 'path'
    (string that lists directories separated by 'os.pathsep';
    defaults to os.environ['PATH']). Checks for all executable
    extensions. Returns full path or None if no command is found.
    """
    if path is None:
        path = os.environ['PATH']
    paths = path.split(os.pathsep)
    extlist = ['']
    if os.name == 'os2':
        (base, ext) = os.path.splitext(executable)
        # executable files on OS/2 can have an arbitrary extension, but
        # .exe is automatically appended if no dot is present in the name
        if not ext:
            executable = executable + ".exe"
    elif sys.platform == 'win32':
        pathext = os.environ['PATHEXT'].lower().split(os.pathsep)
        (base, ext) = os.path.splitext(executable)
        if ext.lower() not in pathext:
            extlist = pathext
        # Windows looks for binaries in current dir first
        paths.insert(0, '')

    for ext in extlist:
        execname = executable + ext
        for p in paths:
            f = os.path.join(p, execname)
            if os.path.isfile(f):
                return f
    else:
        return None

if __name__ == '__main__':
    if sys.argv[1:]:
        print(find_executable(sys.argv[1]))
    else:
        print('usage: find_executable.py <progname>')

Added a link to shutil.which for Python 3 users.