docs: def git_version():
      """Constructs a version string of the form:
  
             <tag>[.<distance-from-tag>[+<branch-name-if-not-master>]]
  
         Master is understood to be always buildable and thus untagged
         versions are treated as patch levels. Branches not master are treated
         as PEP-440 "local version identifiers".
      """
      tag = cmd('git', 'describe').strip()
      pieces = s(tag).split('-')
      dotted = pieces[0]
      if len(pieces) < 2:
          distance = None
      else:
          # Distance from the latest tag is treated as a patch level.
          distance = pieces[1]
          dotted += '.' + s(distance)
      # Branches that are not master are treated as local:
      #   https://www.python.org/dev/peps/pep-0440/#local-version-identifiers
      if distance is not None:
          branch = get_git_branch()
          if branch != 'master':
              dotted += '+' + s(branch)
      return dotted