[python] evaluate None type value

[GergelyMolnar]

I'm having trouble figuring out how to effectively test against None type. I mean when a variable/dict-key has the value of None.

Here's a simple snippet

from durable.lang import *

jj = {'v': None}

with ruleset('getNone1'):
    @when_all(-m.v)
    def isNone_4(c):
        print('isNone_4')

with ruleset('getNone2'):
    @when_all(none(+m.v))
    def isNone_3(c):
        print('isNone_3')

# both post causes infinite loop
post('getNone1', jj)
post('getNone2', jj)

Both post() calls causing an infinite loop printing the given message endlessly (isNone_4/isNone_3).

m.v == None doesn't work either.

What's the proposed way to check against None value especially in combination with other values in the same clause.

Thanks for the help in advance! Gergely

[jruizgit]

Hi, thanks for asking this question. + and - are used for testing the existence of a field. none() is used for testing the existence of a fact (typically to filter out correlated facts). Testing for None should be done explicitly using != and ==. That said, as I tested your scenario I found a bug. I broke the JSON nil test when refactoring the 2.0.x engine. I have pushed a fix, please use version 2.0.19. The following scenario will work as expected:

with ruleset('none_test'):
    @when_all(m.v == None)
    def is_none(c):
        print('none_test passed')

post('none_test', {'v': None})
try:
    post('none_test', {'v': 'something'})
except BaseException as e:
    print('none_test -> expected {0}'.format(e.message))

[GergelyMolnar]

2.0.19 works like a charm. Thanks a lot!