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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def list_policy_versions(policy_name,
                  region=None, key=None, keyid=None, profile=None):
    '''
    List versions of a policy.

    CLI Example:

    .. code-block:: bash

        salt myminion boto_iam.list_policy_versions mypolicy
    '''
    conn = _get_conn(region=region, key=key, keyid=keyid, profile=profile)

    policy_arn = _get_policy_arn(policy_name, region, key, keyid, profile)
    try:
        ret = conn.list_policy_versions(policy_arn)
        return ret.get('list_policy_versions_response', {}).get('list_policy_versions_result', {}).get('versions')
    except boto.exception.BotoServerError as e:
        log.debug(e)
        log.error('Failed to list versions for IAM policy %s.', policy_name)
        return []