<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def _rev(repo):
    '''
    Returns revision ID of repo
    '''
    try:
        repo_info = dict(six.iteritems(CLIENT.info(repo['repo'])))
    except (pysvn._pysvn.ClientError, TypeError,
            KeyError, AttributeError) as exc:
        log.error(
            'Error retrieving revision ID for svnfs remote %s '
            '(cachedir: %s): %s',
            repo['url'], repo['repo'], exc
        )
    else:
        return repo_info['revision'].number
    return None