#15 Exception when using kwargs for a topic listener

[RediZ]

Hi, I'm using PyPubSub v3.3 and the example declared here [1] gives me an error. (see below the whole trace)

http://pubsub.sourceforge.net/usage/usage_advanced_other.html#receiving-all-data-of-a-topic

===== Trace =====
$ python
Python 2.7.6 (default, Jan  6 2014, 12:07:35) 
[GCC 4.2.1 Compatible Apple LLVM 5.0 (clang-500.2.79)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from pubsub import pub
>>> def listener(**kwargs): print 'listener: ', kwargs
... 
>>> pub.subscribe(listener, 'topic')
(<pubsub.core.listenerimpl.Listener instance="" at="" 0x1069f3710="">, True)
>>> pub.sendMessage('topic', test='foo')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "pubsub/core/kwargs/publisher.py", line 27, in sendMessage
    topicObj.publish(**kwargs)
  File "pubsub/core/kwargs/publishermixin.py", line 24, in publish
    self._publish(msgKwargs)
  File "pubsub/core/topicobj.py", line 375, in _publish
    iterState = self._mix_prePublish(data)
  File "pubsub/core/kwargs/publishermixin.py", line 49, in _mix_prePublish
    iterState.checkMsgArgs( self._getListenerSpec() )
  File "pubsub/core/kwargs/publishermixin.py", line 34, in checkMsgArgs
    spec.check(self.filteredArgs)
  File "pubsub/core/kwargs/topicargspecimpl.py", line 125, in check
    py2and3.keys(msgKwargs), optional - set(self.allOptional) )
pubsub.core.topicargspecimpl.SenderUnknownMsgDataError: Some optional args unknown in call to sendMessage('('topic',)', test): test

[RediZ]

This was on osx Mavericks, but I imagine the behavior should be consistent
across this version of python (?)
On Mar 22, 2014 9:24 AM, "schoenborno" schoenborno@users.sf.net wrote:

• status: open --> accepted
• assigned_to: schoenborno
• Comment:

Interesting, because this functionality is tested in the
root/tests/pubsub_kwargs/test1_listener.py and
tests\pubsub_kwargs\test3c_pubsub3.py and thoses tests pass on Windows,
OSXhttp://jeromelaheurte.net:8200/builders/osx/builds/55/steps/tests/logs/stdioand Linux. What is you platform, the python header indicates Darwin can you
get specifically what it is?

---

• [bugs:#15] http://sourceforge.net/p/pubsub/bugs/15/ Exception when
  using kwargs for a topic listener*

Status: accepted
Group: v3.2.0
Created: Tue Mar 11, 2014 11:22 PM UTC by RediZ
Last Updated: Tue Mar 11, 2014 11:22 PM UTC
Owner: schoenborno

Hi, I'm using PyPubSub v3.3 and the example declared here [1] gives me an
error. (see below the whole trace)

http://pubsub.sourceforge.net/usage/usage_advanced_other.html#receiving-all-data-of-a-topic

===== Trace =====
$ python
Python 2.7.6 (default, Jan 6 2014, 12:07:35)
[GCC 4.2.1 Compatible Apple LLVM 5.0 (clang-500.2.79)] on darwin
Type "help", "copyright", "credits" or "license" for more information.

from pubsub import pub
def listener(**kwargs): print 'listener: ', kwargs
...
pub.subscribe(listener, 'topic')
(, True)
pub.sendMessage('topic', test='foo')
Traceback (most recent call last):
File "", line 1, in
File "pubsub/core/kwargs/publisher.py", line 27, in sendMessage
topicObj.publish(**kwargs)
File "pubsub/core/kwargs/publishermixin.py", line 24, in publish
self._publish(msgKwargs)
File "pubsub/core/topicobj.py", line 375, in _publish
iterState = self._mix_prePublish(data)
File "pubsub/core/kwargs/publishermixin.py", line 49, in _mix_prePublish
iterState.checkMsgArgs( self._getListenerSpec() )
File "pubsub/core/kwargs/publishermixin.py", line 34, in checkMsgArgs
spec.check(self.filteredArgs)
File "pubsub/core/kwargs/topicargspecimpl.py", line 125, in check
py2and3.keys(msgKwargs), optional - set(self.allOptional) )
pubsub.core.topicargspecimpl.SenderUnknownMsgDataError: Some optional args unknown in call to sendMessage('('topic',)', test): test

---

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[schoenborno]

Interesting, because this functionality is tested in the root/tests/pubsub_kwargs/test1_listener.py and tests\pubsub_kwargs\test3c_pubsub3.py and thoses tests pass on Windows, OSX and Linux. What is you platform, the python header indicates Darwin can you get specifically what it is?

[schoenborno]

Actually this is not a bug in the code, only in the documentation.

The reason this happens is that pypubsub verifies that listeners and messages are "compatible" in their keyword arguments. Unless there is a topic message data specification that defines the given topic, pypubsub infers it based on the first sendMessage (via the keyword arguments provided) or listener subscription (via the listener's arguments), whichever comes first. But **kwargs is a catch-all, it defines a "generic listener" that can be used for any topic that has the arguments that come before it.

So pypubsub infers from your lines of code, that all messages for topic "topic" have no data whatsoever (since there is nothing before the **kwargs). So when you sendMessage with a "test" data pypubsub says, rightfully, that the topic does not accept this data.

The example implicitly assumes that the topic has already been subscribed to by a non-generic listener. I should update the docs with this info, and fix the example to show this:

def listener1(arg1=1, arg2=2): print 'listener1'
def listener2(**kwargs): print 'listener2'
pub.subscribe(listener1, 'topic')
pub.subscribe(listener2, 'topic')
pub.sendmessage('topic', arg1=123, arg2=456)

So pypubsub does not allow sending arbitrary data. The sender and listener must agree on what can be sent. Is it clear that

pub.sendmessage('topic', notAnArg=1231)

will not work if run after the above code? PyPubSub will not allow it because it is a breach of contract: listeners of "topic" can only handle messages that have arg1 and arg2 fields (or a subset thereof since the listener shows them as optional -- see the docs for this).

[schoenborno]

Fixed the example and added explaination that **kwargs does not get used towards topic specification so need a subscribe or def topic (via provider).