human
Complete this python program:
def find_mrjob_conf():
assistant
#Here is the Python program you requested.

    """Look for :file:`mrjob.conf`, and return its path. Places we look:
    - The location specified by :envvar:`MRJOB_CONF`
    - :file:`~/.mrjob.conf`
    - :file:`/etc/mrjob.conf`
    Return ``None`` if we can\t find it.
    """
    def candidates():
        if ('MRJOB_CONF' in os.environ):
            (yield expand_path(os.environ['MRJOB_CONF']))
        (yield expand_path(os.path.join('~', '.mrjob.conf')))
        (yield '/etc/mrjob.conf')
    for path in candidates():
        log.debug(('Looking    for    configs    in    %s' % path))
        if os.path.exists(path):
            log.info(('Using    configs    in    %s' % path))
            return path
    else:
        log.info('No    configs    found;    falling    back    on    auto-configuration')
        return None