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

[<hg...@it...>]

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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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
look and join the conversation now. http://goparallel.sourceforge.net
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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.