#9 Improve diagnostics for PythonException

[Alexander Tyutyunnik]

When PythonException is thrown, it is not always obvious what might be wrong. For example: the test class does not have the required write() method:

class Test(object):
pass

try:
from jpype import *
startJVM(getDefaultJVMPath())
MyStream_proxy = JClass("MyStream_proxy")
python_adapter = Test()
java_proxy = MyStream_proxy(JProxy("MyStream_adapter", inst = python_adapter))
java_proxy.write(5)

except Exception:
import traceback
traceback.print_exc()

Output:
Traceback (most recent call last):
File "F:\temp\jpype\bugs\3-NonInformativeErrorMessage\test.py", line 10, in ?
java_proxy.write(5)
java.lang.ExceptionPyRaisable: java.lang.RuntimeException: Python exception thrown

The exception thrown by Python code is lost.

[Alexander Tyutyunnik]

test.py

[Alexander Tyutyunnik]

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File Added: test.py

[Alexander Tyutyunnik]

MyStream_proxy.java

[Alexander Tyutyunnik]

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user_id=1558596
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File Added: MyStream_proxy.java

[Alexander Tyutyunnik]

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user_id=1558596
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Proposed hack (I do not know how to extend the traceback information):
PythonException::PythonException()
{
...
PyErr_Fetch(&m_ExceptionClass, &m_ExceptionValue, &traceback);
//This PyErr_Display() is added for better diagnostics,
//for some reason PyErr_Restore() does not restore the full traceback stack
PyErr_Display(m_ExceptionClass, m_ExceptionValue, traceback);
Py_INCREF(m_ExceptionClass);
Py_INCREF(m_ExceptionValue);
...