# Problem with unicode characters (e.g. →) in prolog file on swiplserver **URL:** \ **Category:** Help!\ **Created:** [January 27, 2022, 10:56am UTC](https://swi-prolog.discourse.group/t/problem-with-unicode-characters-e-g-in-prolog-file-on-swiplserver/4945 "2022-01-27T10:56:21Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Losbarthos](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/losbarthos/32/4037_2.png) [@Losbarthos](https://swi-prolog.discourse.group/u/Losbarthos)\ **Post date:** [January 27, 2022, 10:56am UTC](https://swi-prolog.discourse.group/t/problem-with-unicode-characters-e-g-in-prolog-file-on-swiplserver/4945/1 "2022-01-27T10:56:21Z")
I have some simple prolog file logic.pl introducing some operator with unicode characters: ```prolog :-op(803, xfy, →). binary_connective(X → Y, X, Y). ``` The problem now is, that my python query does not work on that operator: ```prolog from swiplserver import PrologMQI, PrologThread with PrologMQI() as mqi: with mqi.create_thread() as prolog_thread: prolog_thread.query(f"consult('logic.pl').") prolog_thread.query_async("binary_connective(p → q, X, Y).", find_all=False) while True: result = prolog_thread.query_async_result() if result is None: break else: print(result) ``` If I change → in – it gives me some working result. Is their some way to solve this in swiplserver libary? I also made some post on this site ([Problem with unicode characters (e.g. →) in prolog file · Issue #14 · SWI-Prolog/packages-mqi · GitHub](https://github.com/SWI-Prolog/packages-mqi/issues/14)) ---
**Author:** ![ericzinda](https://avatars.discourse-cdn.com/v4/letter/e/b3f665/32.png) [@ericzinda](https://swi-prolog.discourse.group/u/ericzinda)\ **Post date:** [January 27, 2022, 5:45pm UTC](https://swi-prolog.discourse.group/t/problem-with-unicode-characters-e-g-in-prolog-file-on-swiplserver/4945/3 "2022-01-27T17:45:19Z")
> [@Losbarthos](#): > > that my python query does not work on that operator: What is the error you see when you run the query from Python? Also: Does it work if you run it from the top level (it should (almost) always work the same if you are using the MQI library)? I.e.: ```prolog ?- consult('logic.pl'). true ?- binary_connective(p → q, X, Y). ???? ``` Edit: If I try putting your code, exactly as you have it above, in a `logic.pl` file and consulting it, I get the following error. I may have missed some magic unicode incantation though, I haven’t done anything with unicode and SWI Prolog before: ```prolog ERROR: logic.pl:1:17: Syntax error: illegal_character ERROR: logic.pl:3:21: Syntax error: Operator expected true. ``` ---
**Author:** ![Losbarthos](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/losbarthos/32/4037_2.png) [@Losbarthos](https://swi-prolog.discourse.group/u/Losbarthos)\ **Post date:** [January 27, 2022, 9:04pm UTC](https://swi-prolog.discourse.group/t/problem-with-unicode-characters-e-g-in-prolog-file-on-swiplserver/4945/4 "2022-01-27T21:04:34Z")
Hello, thank you for your response. I don’t get some error if I put the predicate directly into swipl with SWI-Prolog version 8.2.4 for x86\_64-linux. My prolog file simply contains the following content ```prolog :-op(803, xfy, →). binary_connective(X → Y, X, Y). ``` My output in swipl is: ```prolog ?- consult('logic.pl'). true. ?- binary_connective(p → q, X, Y). X = p, Y = q. ``` I also tested it on [https://swish.swi-prolog.org/](https://swish.swi-prolog.org/) and it worked exactly the same. If I run the query from Python I don’t get some error. It seems the program stucks at some point in some endless loop. How can I run the program from toplevel? Did you mean use: ```prolog from swiplserver import PrologServer, PrologThread with PrologServer() as server: with server.create_thread() as prolog_thread: prolog_thread.query("consult('logic.pl').") result = prolog_thread.query("binary_connective(p → q, X, Y).") print(result) ``` This doesn’t work, cause of error ImportError: cannot import name ‘PrologServer’ from ‘swiplserver’ (/home/~/.local/lib/python3.9/site-packages/swiplserver/ **init**.py) It seams the ` __init__.py` looks like this: ```prolog from swiplserver.prologmqi import ( PrologMQI, PrologThread, PrologError, PrologLaunchError, PrologQueryTimeoutError, PrologQueryCancelledError, PrologConnectionFailedError, PrologResultNotAvailableError, PrologNoQueryError, is_prolog_variable, is_prolog_list, is_prolog_functor, is_prolog_atom, create_posix_path, prolog_name, prolog_args, quote_prolog_identifier, json_to_prolog, ) # make "from swiplserver import *" work __all__ = [ "PrologLaunchError", "PrologQueryTimeoutError", "PrologQueryCancelledError", "PrologConnectionFailedError", "PrologResultNotAvailableError", "PrologNoQueryError", "PrologError", "PrologMQI", "PrologThread", "create_posix_path", "is_prolog_functor", "is_prolog_list", "is_prolog_variable", "is_prolog_atom", "prolog_name", "prolog_args", "quote_prolog_identifier", "json_to_prolog", ] ``` ---
**Author:** ![ericzinda](https://avatars.discourse-cdn.com/v4/letter/e/b3f665/32.png) [@ericzinda](https://swi-prolog.discourse.group/u/ericzinda)\ **Post date:** [January 27, 2022, 11:15pm UTC](https://swi-prolog.discourse.group/t/problem-with-unicode-characters-e-g-in-prolog-file-on-swiplserver/4945/5 "2022-01-27T23:15:22Z")
> [@Losbarthos](#): > > I don’t get some error if I put the predicate directly into swipl I am able to replicate the hang you are hitting on my mac if I do the below. On my mac, at least, I need to set the Prolog encoding to utf8 in order to load the `logic.pl` file properly: ```prolog with PrologMQI() as mqi: with mqi.create_thread() as prolog_thread: prolog_thread.query(f"set_prolog_flag(encoding,utf8).") prolog_thread.query(f"consult('logic.pl').") unicode = "binary_connective(p → q, X, Y)." prolog_thread.query(unicode) ``` The problem is a bug in the swiplserver library that sends the wrong count of characters to Prolog. I was able to fix the hang with the below change to the prologmqip.py file that is part of the library. I need to do some more research to make sure this is a good overall fix but I think it should unblock you for the moment. I’ll post when I have the final fix. ```prolog def _send(self, value): value = value.strip() value = value.rstrip("\n.") value += ".\n" _log.debug("PrologMQI send: %s", value) utf8Value = value.encode("utf-8") # Comment out this line: # msgHeader = f"{str(len(utf8Value))}.\n".encode("utf-8") # Replace with this line: msgHeader = f"{str(len(value))}.\n".encode("utf-8") self._socket.sendall(msgHeader) self._socket.sendall(utf8Value) ``` ---
**Author:** ![Losbarthos](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/losbarthos/32/4037_2.png) [@Losbarthos](https://swi-prolog.discourse.group/u/Losbarthos)\ **Post date:** [January 28, 2022, 11:34am UTC](https://swi-prolog.discourse.group/t/problem-with-unicode-characters-e-g-in-prolog-file-on-swiplserver/4945/6 "2022-01-28T11:34:25Z")
Thank you, with that replacement it seems to be correct for me too. ---
**Author:** ![ericzinda](https://avatars.discourse-cdn.com/v4/letter/e/b3f665/32.png) [@ericzinda](https://swi-prolog.discourse.group/u/ericzinda)\ **Post date:** [January 29, 2022, 12:54am UTC](https://swi-prolog.discourse.group/t/problem-with-unicode-characters-e-g-in-prolog-file-on-swiplserver/4945/7 "2022-01-29T00:54:56Z")
I have submitted a more comprehensive fix to both the server and the Python client, but the client fix is basically what I posted above, the submitted fix just works against the existing MQI interface and the new fixed one. It also includes a really simple protocol versioning “feature” to more robustly handle versioning issues going forward. I’ll push the Python library 1.0.2 to [pypi.org](http://pypi.org) early next week. > > > Details in: https://github.com/SWI-Prolog/packages-mqi/issues/14 > > The MQI implem…entation had a bug where sends to MQI expected the message header to provide a count of Unicode code points instead of what it should have been: UTF8 bytes. This has been corrected but is a breaking change, so: > > ADDED: A simple protocol versioning interface to the MQI. There is now a mqi\_version/2 predicate and the MQI returns Major and Minor version in its response to an initial connect message. > > ADDED: The swiplserver Python library properly detects the original and fixed versions and works against both of them. > > TEST: Added tests for multi-byte UTF8 characters ---
**Author:** ![jan](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/jan/32/4_2.png) [@jan](https://swi-prolog.discourse.group/u/jan)\ **Post date:** [January 29, 2022, 8:26am UTC](https://swi-prolog.discourse.group/t/problem-with-unicode-characters-e-g-in-prolog-file-on-swiplserver/4945/8 "2022-01-29T08:26:35Z")
Thanks! Updated the git submodule. ---
**Author:** ![Losbarthos](https://yyz2.discourse-cdn.com/free1/user_avatar/swi-prolog.discourse.group/losbarthos/32/4037_2.png) [@Losbarthos](https://swi-prolog.discourse.group/u/Losbarthos)\ **Post date:** [January 30, 2022, 1:12pm UTC](https://swi-prolog.discourse.group/t/problem-with-unicode-characters-e-g-in-prolog-file-on-swiplserver/4945/9 "2022-01-30T13:12:34Z")
Thank you I have closed the GitHub issue. ---
**Author:** ![ericzinda](https://avatars.discourse-cdn.com/v4/letter/e/b3f665/32.png) [@ericzinda](https://swi-prolog.discourse.group/u/ericzinda)\ **Post date:** [January 31, 2022, 7:38pm UTC](https://swi-prolog.discourse.group/t/problem-with-unicode-characters-e-g-in-prolog-file-on-swiplserver/4945/10 "2022-01-31T19:38:47Z")
Thanks! You can now `pip install swiplserver` and get the latest version (1.0.2) with the above fix in it. > **[swiplserver](https://pypi.org/project/swiplserver/1.0.2/)** > > swiplserver integrates SWI Prolog with Python.