find the location of an executable

def which(executable):
    """find the location of an executable"""
    locations = (
        '/usr/local/bin',
        '/bin',
        '/usr/bin',
        '/usr/local/sbin',
        '/usr/sbin',
        '/sbin',
    )

    for location in locations:
        executable_path = os.path.join(location, executable)
        if os.path.exists(executable_path) and os.path.isfile(executable_path):
            return executable_path