def snapshot_versioning(version_info):
    """ Just use the pep440-validated tag-version and add -SNAPSHOT if git is dirty.

        >>> snapshot_versioning({'vcs_info': {}})
        >>> snapshot_versioning({'vcs_info': {'dirt': ' M flowtool_versioning/dropins/version.py\\n', 'prefix_tag_distances': {'flowtool-versioning-0.7.33': 53, 'flowtool-versioning-0.7.32': 134, 'flowtool-versioning-0.7.34': 37}, 'tag_version': {'normalized': '0.7.34', 'version': '0.7.34', 'release': (0, 7, 34)}, 'latest_tag': 'flowtool-versioning-0.7.34', 'latest_tag_version': '0.7.34', 'latest_tag_commit': 'b25974fb03e02f491ace23d2718a847a6d01853d', 'commit': 'a06e7d03436457883e2bce2ebe7968886943e2bb', 'prefix': 'flowtool-versioning-'}, 'version': '0.7.34+37.git:b25974fb.dirty'})
        '0.7.34-SNAPSHOT'
    """
    if not 'tag_version' in version_info['vcs_info']:
        return
    version = version_info['vcs_info']['tag_version']['version']
    if version_info['vcs_info']['dirt']:
        version += '-SNAPSHOT'
    return version
