Return a constant describing the status of the given package
    or collection.  Status can be one of ``INSTALLED``,
    ``NOT_INSTALLED``, ``STALE``, or ``PARTIAL``.

def status(self, info_or_id, download_dir=None):
    """
    Return a constant describing the status of the given package
    or collection.  Status can be one of ``INSTALLED``,
    ``NOT_INSTALLED``, ``STALE``, or ``PARTIAL``.
    """
    if download_dir is None: download_dir = self._download_dir
    info = self._info_or_id(info_or_id)

    # Handle collections:
    if isinstance(info, Collection):
      pkg_status = [self.status(pkg.id) for pkg in info.packages]
      if self.STALE in pkg_status:
        return self.STALE
      elif self.PARTIAL in pkg_status:
        return self.PARTIAL
      elif (self.INSTALLED in pkg_status and
          self.NOT_INSTALLED in pkg_status):
        return self.PARTIAL
      elif self.NOT_INSTALLED in pkg_status:
        return self.NOT_INSTALLED
      else:
        return self.INSTALLED

    # Handle packages:
    else:
      filepath = os.path.join(download_dir, info.filename)
      if download_dir != self._download_dir:
        status = self._pkg_status(info, filepath)
      else:
        if info.id not in self._status_cache:
          self._status_cache[info.id] = self._pkg_status(info,
                                   filepath)
        return self._status_cache[info.id]