Re: [Py4j-users] How can I pass a List<short> or List<byte> from Python to Java?

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Thanks for the quick response, Barthelemy! For now I'll pursue the shim
route, but I'll keep an eye out of #163 to be resolved.

On Tue, Jul 14, 2015 at 8:25 PM Barthelemy Dagenais <bar...@in...>
wrote:

> After some investigation, there is no easy or quick solution because of
> the difference in the type systems and the autoboxing behavior of Java.
> From a design perspective, I'm pretty sure converting primitives such as
> short to Python int is saner than trying to track the original primitive
> type. Preventing primitive wrapper (such as Byte and Short) from being
> converted to Python int though makes a lot of sense, but requires a few non
> trivial changes.
>
> It's doable and I have a plan, but it won't be available before a few
> weeks, so your best bet on the short term is to rely on a Java shim or a
> third party library.
>
> Link to Github issue for reference:
> https://github.com/bartdag/py4j/issues/163
>
> Barthelemy
>
> On Tue, Jul 14, 2015 at 2:26 PM Dan O'Reilly <ore...@gm...> wrote:
>
>> It seems that on the Python side, Py4J will automatically convert the
>> java type short (and byte) to the Python type int, which means there's no
>> way to pass a List<short> from Python to Java. Consider this example:
>>
>> import java.util.List;
>>
>> import py4j.GatewayServer;
>>
>> class Test {
>>
>>     public void testByte(List<Byte> l) {
>>         Byte i = l.get(0);
>>     }
>>
>>     public static void main(String[] args) {
>>         GatewayServer gw = new GatewayServer(new Test());
>>         gw.start();
>>         System.out.println("GatewayServer started...");
>>     }
>> }
>>
>> If I try to call testByte from the Python side, I seem to get an
>> ClassCastException no matter what I try:
>>
>> >>> gw = JavaGateway()
>> >>> z = ListConverter().convert([1,2], gw._gateway_client)
>> >>> gw.entry_point.testByte(z)
>> Traceback (most recent call last):
>>   File "<stdin>", line 1, in <module>
>>   File "/usr/local/lib/python2.7/dist-packages/py4j/java_gateway.py",
>> line 538, in __call__
>>     self.target_id, self.name)
>>   File "/usr/local/lib/python2.7/dist-packages/py4j/protocol.py", line
>> 300, in get_return_value
>>     format(target_id, '.', name), value)
>> py4j.protocol.Py4JJavaError: An error occurred while calling t.testByte.
>> : java.lang.ClassCastException: java.lang.Integer cannot be cast to
>> java.lang.Byte
>> at Test.testByte(Test.java:8)
>> 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:497)
>> 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)
>>
>>
>> >>> z =
>> ListConverter().convert([gw.jvm.java.lang.Byte(1),gw.jvm.java.lang.Byte(2)],
>> gw._gateway_client)
>> >>> gw.entry_point.testByte(z)
>> Traceback (most recent call last):
>>   File "<stdin>", line 1, in <module>
>>   File "/usr/local/lib/python2.7/dist-packages/py4j/java_gateway.py",
>> line 538, in __call__
>>     self.target_id, self.name)
>>   File "/usr/local/lib/python2.7/dist-packages/py4j/protocol.py", line
>> 300, in get_return_value
>>     format(target_id, '.', name), value)
>> py4j.protocol.Py4JJavaError: An error occurred while calling t.testByte.
>> : java.lang.ClassCastException: java.lang.Integer cannot be cast to
>> java.lang.Byte
>> at Test.testByte(Test.java:8)
>> 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:497)
>> 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)
>>
>> Is there some way to work around this? Ideally there would be away
>> without having to make changes on the Java-side, since for my actual
>> use-case I'm trying to call into an API I don't control. I could probably
>> make things work if I needed to call a Java shim instead, but I'd really
>> like to avoid that.
>>
>> Thanks,
>> Dan O'Reilly
>>
>>
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