code: def get_versions():
      
      # I am in _version.py, which lives at ROOT/VERSIONFILE_SOURCE. If we have
      # __file__, we can work backwards from there to the root. Some
      # py2exe/bbfreeze/non-CPython implementations don't do __file__, in which
      # case we can only use expanded keywords.
  
      cfg = get_config()
      verbose = cfg.verbose
  
      try:
          return git_versions_from_keywords(get_keywords(), cfg.tag_prefix,
                                            verbose)
      except NotThisMethod:
          pass
  
      try:
          root = os.path.realpath(__file__)
          # versionfile_source is the relative path from the top of the source
          # tree (where the .git directory might live) to this file. Invert
          # this to find the root from __file__.
          for i in cfg.versionfile_source.split('/'):
              root = os.path.dirname(root)
      except NameError:
          return {"version": "0+unknown", "full-revisionid": None,
                  "dirty": None,
                  "error": "unable to find root of source tree"}
  
      try:
          pieces = git_pieces_from_vcs(cfg.tag_prefix, root, verbose)
          return render(pieces, cfg.style)
      except NotThisMethod:
          pass
  
      try:
          if cfg.parentdir_prefix:
              return versions_from_parentdir(cfg.parentdir_prefix, root, verbose)
      except NotThisMethod:
          pass
  
      _version_path = os.path.join(os.path.dirname(__file__), '_version')
      if os.path.exists(_version_path):
          with open(_version_path) as f:
              l = f.readline().strip()
              return {
                  'version': l,
                  'error': None,
                  'dirty': None,
                  'full-revisionid': l
              }
  
      return {"version": "0+unknown", "full-revisionid": None,
              "dirty": None,
              "error": "unable to compute version"}
docs: Get version information or return default if unable to do so.