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https://issues.apache.org/jira/browse/PIG-2098?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13039803#comment-13039803
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Woody Anderson commented on PIG-2098:
-------------------------------------
to be clear on the parans issue, Nicolas Torzec cleared that up:
In Python, a tuple is recognized by the commas that separate its elements, not
by its surrounding parenthesis, which are just used for grouping expressions...
That’s why both “t = (key, )” and “t = key, ” work, but not “t = (key)”.
Nicolas.
> jython - problem with single item tuple in bag
> ----------------------------------------------
>
> Key: PIG-2098
> URL: https://issues.apache.org/jira/browse/PIG-2098
> Project: Pig
> Issue Type: Bug
> Affects Versions: 0.8.1, 0.9.0
> Reporter: Vivek Padmanabhan
> Assignee: Woody Anderson
>
> While using phython udf, if I create a tuple with a single field, Pig
> execution fails with ClassCastException.
> Caused by: java.io.IOException: Error executing function:
> org.apache.pig.backend.executionengine.ExecException: ERROR 0: Cannot convert
> jython type to pig datatype java.lang.ClassCastException: java.lang.String
> cannot be cast to org.apache.pig.data.Tuple
> at
> org.apache.pig.scripting.jython.JythonFunction.exec(JythonFunction.java:111)
> at
> org.apache.pig.backend.hadoop.executionengine.physicalLayer.expressionOperators.POUserFunc.getNext(POUserFunc.java:245)
> An example to reproduce the issuue ;
> Pig Script
> {code}
> register 'mapkeys.py' using jython as mapkeys;
> A = load 'mapkeys.data' using PigStorage() as ( aMap: map[] );
> C = foreach A generate mapkeys.keys(aMap);
> dump C;
> {code}
> mapkeys.py
> {code}
> @outputSchema("keys:bag{t:tuple(key:chararray)}")
> def keys(map):
> print "mapkeys.py:keys:map:", map
> outBag = []
> for key in map.iterkeys():
> t = (key) ## doesn't work, causes Pig to crash
> #t = (key,) ## adding empty value works :-/
> outBag.append(t)
> print "mapkeys.py:keys:outBag:", outBag
> return outBag
> {code}
> Input data 'mapkeys.data'
> [name#John,phone#5551212]
> In the udf, t = (key) , because of this the item inside the bag is treated as
> a string instead of a tuple which causes for the class cast execption.
> If I provide an additional comma, t = (key,) , then the script goes through
> fine.
> From code what I can see is that ,for "t = (key,)" , pythonToPig(..) recieves
> the pyObject as [(u'name',), (u'phone',)] from the PyFunction call .
> But for "t = (key)" the return from PyFunction call is [u'name', u'phone']
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