Re: [Py4j-users] 回覆: Exception when printing a returned List<String> object

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Hi,

apologies for the delays :-)

The behavior you are seeing is strange.

Here are a few pointers:

a) Error Logging can be turned on and off on both sides:
http://py4j.sourceforge.net/faq.html#how-to-turn-logging-on-off

b) Which version of py4j, python, and Java are you using?

c) Are you able to print a standard list, e.g., ArrayList? e.g.,

a_list = gateway.jvm.java.util.ArrayList()
a_list.append("a")
a_list.append("b")
print(a_list)

d) The exceptions you shown seems to come from the JVM. Do you see any
exception on the Python side?

Regards,
Barthelemy

On Tue, Dec 23, 2014 at 9:56 PM,  <hg...@it...> wrote:
> Hi,
>
> Yes, it prints <class 'py4j.java_collections.JavaIterator'>.
> So couldn't I directly assign the return List<String> to a python list like the following and then print it?
>
>>>>ret = []
>>>>ret = gateway.entry_point.getMyStringList(inputStr)
>>>>print ret
>
> If that's the case, for now my workaround for this is below:
>
>>>>ans = [ret[i] for i in range(len(ret))]
>
> and then use "ans" instead.
>
> Could you have any suggestion on this otherwise?
>
> Besides, because the exception message only appears partially, how can I log full error messages and debug when the server stops? I think it's especially necessary when the error behavior is in the server side.
>
> Thanks,
> Frank Yang
> ________________________________________
> 從: Barthelemy Dagenais <bar...@in...>
> 寄件日期: 2014年12月23日 21:14
> 至: Support and Comments about Py4J
> 主旨: Re: [Py4j-users] Exception when printing a returned List<String>    object
>
> Hi,
>
> When printing the list, Py4J retrieves an Iterator and wraps it with
> py4j.java_collections.JavaIterator. It then cycles through the list
> with the iterator. JavaIterator should catch the
> NoSuchElementException and raise instead a StopIteration. Because it
> does not, I suspect something is messing with the automated wrapping
> of collections.
>
> could you do:
>
> iter = ret.iterator()
> print(type(iter))
>
> This should print something like <class 'py4j.java_collections.JavaIterator'>
>
> Thanks,
> Barthelemy
>
> On Tue, Dec 23, 2014 at 6:10 AM,  <hg...@it...> wrote:
>> Hi,
>>
>>
>> The method in my gateway server will return a List<String> object. When I
>> access it in my python client code, the server has exception and then
>> closed. The following is part of the exceptions
>>
>>
>>
>>
>> ▒Q▒G▒▒ 23, 2014 5:18:14 ▒U▒▒ py4j.reflection.MethodInvoker invoke
>> ĵ▒i: Exception occurred in client code.
>> java.lang.reflect.InvocationTargetException
>>         at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
>>         at
>> sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
>>         at
>> sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
>>         at java.lang.reflect.Method.invoke(Method.java:483)
>>         at py4j.reflection.MethodInvoker.invoke(MethodInvoker.java:231)
>>         at
>> py4j.reflection.ReflectionEngine.invoke(ReflectionEngine.java:379)
>>         at py4j.Gateway.invoke(Gateway.java:259)
>>         at
>> py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:133)
>>         at py4j.commands.CallCommand.execute(CallCommand.java:79)
>>         at py4j.GatewayConnection.run(GatewayConnection.java:207)
>>         at java.lang.Thread.run(Thread.java:745)
>> Caused by: java.util.NoSuchElementException
>>         at java.util.AbstractList$Itr.next(AbstractList.java:364)
>>         ... 11 more
>>
>> What I do in client code is the following:
>>
>>>>>ret = gateway.entry_point.getMyStringList(inputStr)    # it's ok to run
>>>>> this line
>>>>>print ret       # when running to this line, the server raised exception
>>
>>
>> Below is the method in server side:
>>
>> public List<String> getMyStringList(String input) throws IOException {
>>     List<String> strList = new ArrayList<String>();
>>     strList = segmenter.segmentString(input);    //  this is some 3rd party
>> API for string tokenization and has been tested OK in console, the return
>> object is List<String>
>>
>>     return strList;
>> }
>>
>> It's OK to access "ret" using indices and len(), but when I just type "ret"
>> or "print ret", then it would display the content of "ret", but then the
>> server poped Exception and stopped. What would be the problemt? Thanks for
>> any help!
>>
>>
>>
>> Frank Yang
>>
>>
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>
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> 本信件可能包含工研院機密資訊，非指定之收件者，請勿使用或揭露本信件內容，並請銷毀此信件。
> This email may contain confidential information. Please do not use or disclose it in any way and delete it if you are not the intended recipient.
> ------------------------------------------------------------------------------
> Dive into the World of Parallel Programming! The Go Parallel Website,
> sponsored by Intel and developed in partnership with Slashdot Media, is your
> hub for all things parallel software development, from weekly thought
> leadership blogs to news, videos, case studies, tutorials and more. Take a
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