Implement the Linux `which` command in Python that works in Windows!

which.py

import os

def which(executable):    
    for path in os.environ['PATH'].split(os.pathsep):
        path = path.strip('"')

        fpath = os.path.join(path, executable)

        if os.path.isfile(fpath) and os.access(fpath, os.X_OK):
            return fpath

    # checks if os is windows and appends .exe extension to
    # `executable`, if not alread present, and rechecks.
    if os.name == 'nt' and not executable.endswith('.exe'):
        return which('{}.exe'.format(executable))

    return None
    
# tested on windows 8.1
print which('python') # C:\Python27\python.exe