docs: def version_diff(version1, version2):
      """Return string representing the diff between package versions.
  
      We're interested in whether this is a major, minor, patch or 'other'
      update. This method will compare the two versions and return None if
      they are the same, else it will return a string value indicating the
      type of diff - 'major', 'minor', 'patch', 'other'.
  
      Args:
          version1: the Version object we are interested in (e.g. current)
          version2: the Version object to compare against (e.g. latest)
  
      Returns a string - 'major', 'minor', 'patch', 'other', or None if the
          two are identical.
  
      """
      if version1 is None or version2 is None:
          return 'unknown'
      if version1 == version2:
          return 'none'
  
      for v in ('major', 'minor', 'patch'):
          if getattr(version1, v) != getattr(version2, v):
              return v
  
      return 'other'