docs: def open(filename):
          """Open (if necessary) filename, and read the magic."""
          if isinstance(filename, six.string_types):
              try:
                  fdesc = gzip.open(filename, "rb")
                  magic = fdesc.read(4)
              except IOError:
                  fdesc = open(filename, "rb")
                  magic = fdesc.read(4)
          else:
              fdesc = filename
              filename = getattr(fdesc, "name", "No name")
              magic = fdesc.read(4)
          return filename, fdesc, magic