Question

I’m finding it very difficult to develop with PyClips, because it appears to replace useful error messages thrown by Clips with a generic “syntax error” message. This makes debugging very laborious and practically impossible on large codebases when using PyClips.

Consider the following example. I wrote a very large expression, which contained the multiplication operator, but I mistakenly forgot to add the second argument. Instead of simply telling I was missing an argument, PyClips told me there was a syntax error. What should have taken me 1 second to correct, took me 5 minutes to correct as I hunted through my large expression, looking for the mistake.

Here’s a condensed version:

In Clips, with a useful error message:

clips
CLIPS> (defrule myrule "" (myfact 123) => (bind ?prob (* (min 1 2))))
[ARGACCES4] Function * expected at least 2 argument(s)

ERROR:
(defrule MAIN::myrule ""
   (myfact 123)
   =>
   (bind ?prob (* (min 1 2))

And in PyClips, with an unuseful error message:

python
>>> import clips
>>> clips.BuildRule('myrule','(myfact 123)','(bind ?prob (* (min 1 2)))','')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.6/dist-packages/clips/_clips_wrap.py", line 2839, in BuildRule
    _c.build(construct)
_clips.ClipsError: C08: syntax error, or unable to parse expression

How can I get PyClips to give me the real error thrown by Clips?

Answer 1

Catch the ClipsError, then read ErrorStream for the details. For example:

engine = clips.Environment()
engine.Reset()
engine.Clear()
try:
    engine.Load(os.path.abspath(rule_file))
except clips.ClipsError:
    logging.error(clips.ErrorStream.Read())