text: import unicodedata
  from typing import Optional
  
  from django.utils.translation import gettext as _
  
  from zerver.lib.exceptions import JsonableError
  from zerver.models import Stream
  
  # There are 66 Unicode non-characters; see
  # https://www.unicode.org/faq/private_use.html#nonchar4
  unicode_non_chars = set(
      chr(x)
      for x in list(range(0xFDD0, 0xFDF0))  # FDD0 through FDEF, inclusive
      + list(range(0xFFFE, 0x110000, 0x10000))  # 0xFFFE, 0x1FFFE, ... 0x10FFFE inclusive
      + list(range(0xFFFF, 0x110000, 0x10000))  # 0xFFFF, 0x1FFFF, ... 0x10FFFF inclusive
  )
  
  
  def check_string_is_printable(var: str) -> Optional[int]:
      # Return position (1-indexed!) of the character which is not
      # printable, None if no such character is present.
      for i, char in enumerate(var):
          unicode_character = unicodedata.category(char)
          if (unicode_character in ["Cc", "Cs"]) or char in unicode_non_chars:
              return i + 1
      return None
  
  
  def check_stream_name(stream_name: str) -> None:
      if stream_name.strip() == "":
          raise JsonableError(_("Stream name can't be empty!"))
  
      if len(stream_name) > Stream.MAX_NAME_LENGTH:
          raise JsonableError(
              _("Stream name too long (limit: {} characters).").format(Stream.MAX_NAME_LENGTH)
          )
      for i in stream_name:
          if ord(i) == 0:
              raise JsonableError(
                  _("Stream name '{}' contains NULL (0x00) characters.").format(stream_name)
              )
  
  
  def check_stream_topic(topic: str) -> None:
      if topic.strip() == "":
          raise JsonableError(_("Topic can't be empty!"))
  
      invalid_character_pos = check_string_is_printable(topic)
      if invalid_character_pos is not None:
          raise JsonableError(
              _("Invalid character in topic, at position {}!").format(invalid_character_pos)
          )
  