code: def is_safe_url(url, host=None):
      
      if url is not None:
          url = url.strip()
      if not url:
          return False
      if six.PY2:  # pragma: nocover
          try:
              url = force_text(url)
          except UnicodeDecodeError:
              return False
      # Chrome treats \ completely as / in paths but it could be part of some
      # basic auth credentials so we need to check both URLs.
      return _is_safe_url(url, host) and _is_safe_url(url.replace('\\', '/'), host)
docs: Return ``True`` if the url is a safe redirection (i.e. it doesn't point to
      a different host and uses a safe scheme).
      Always returns ``False`` on an empty url.