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https://issues.apache.org/jira/browse/FREEMARKER-68?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16123117#comment-16123117
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Daniel Dekany commented on FREEMARKER-68:
-----------------------------------------
The problem is not specific to {{??}} actually. That way it works is that
{{freemarker.ext.jython.JythonModel.get(String)}} is called (which is just an
implementation of {{TemplateHashModel.get(String)}} as far as FreeMarker is
concerned), and then if that returns {{null}} then {{??}} or the other
existence handlers operators (most notably {{exp!defaultExp}}) handle it. That
particular {{get}} implementation calls {{PyObject.__findattr__(key)}}, and if
that returns {{null}} then it also tries {{PyObject.__finditem__(key)}}. If
both was {{null}}, then {{get}} returns {{null}}, and {{??}} works. I'm not
sure what the proper {{PyObject}} calls would be... And frankly, I think that
the Jython wrapper is some early implementation hastily dropped in back then by
the earlier developers, maybe to catch some attention from then much more
active Jython community, but then it was practically abandoned. But as its part
of {{freemarker.jar}}, it stuck there for backward compatibility. So I can
imagine there's a lot to improve there. If anyone cares to improve it (or even
create an external wrapper that's better, as then there are no backward
compatibility constraints), it's highly welcome. Similarly here, it's not
likely that anything will happen without a Pull Request or patch, which also
considers backward compatibility (means, certainly we will need to add
{{incompatibleImprovements}} setting to the {{JythonWrapper}}, similarly as
{{DefaultObjectWrapper}} has it too).
> Double-question mark operator does not properly test for attributes
> -------------------------------------------------------------------
>
> Key: FREEMARKER-68
> URL: https://issues.apache.org/jira/browse/FREEMARKER-68
> Project: Apache Freemarker
> Issue Type: Bug
> Components: engine
> Affects Versions: 2.3.23
> Reporter: Jason Sachs
>
> The double-question mark operator doesn't work properly with some Jython
> objects.
> It works properly with dicts.
> It does not work properly with custom classes and triggers an item lookup.
> Example setup: (I can't post a complete self-contained example, sorry)
> Jython code called before FreeMarker template is rendered:
> {code}
> class VoodooDoll(object):
> def pinch(self):
> return "ouch"
> model['test1'] = dict(voodooDoll=VoodooDoll())
> {code}
> FreeMarker template:
> {code}
> <#if test1.blah??>
> blah present
> </#if>
> <#if test1.voodooDoll??>
> voodoo doll present
> </#if>
> <#if test1.voodooDoll.pinch??>
> voodoo doll pinch present
> </#if>
> <#if test1.voodooDoll.hit??>
> voodoo doll hit present
> </#if>
> {code}
> This produces the output
> {noformat}
> voodoo doll present
> voodoo doll pinch present
> {noformat}
> so the first three {{#if}} tests work properly, but the fourth one causes
> this error:
> {noformat}
> - Failed at: #if test1.voodooDoll.hit?? [in template
> "source\\aux-files\\parameters.html.template" at line 58, column 1]
> ...
> Caused by: TypeError: 'VoodooDoll' object is unsubscriptable
> at org.python.core.Py.TypeError(Py.java:235)
> at org.python.core.PyObject.__finditem__(PyObject.java:585)
> at
> org.python.core.PyObjectDerived.__finditem__(PyObjectDerived.java:861)
> {noformat}
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