Exception chaining/cause not mirrored into Python #1047
Description
Both Python and Java have exception chaining (Throwable.getCause() in Java, exception.__cause__ in Python).
This information doesn't make it across from Java to Python though. Take the following snippet:
import jpype as jp
jp.startJVM()
java = jp.JPackage('java')
e1 = java.lang.RuntimeException("Some parent exception")
e2 = java.lang.RuntimeException("Some message", e1)
When we inspect the object:
>>> print(e2.__cause__, e2.__context__)
None None
>>> raise e2
Traceback (most recent call last):
File "/home/pelson/github/jpype/jpype/support/exception_cause.py", line 19, in <module>
raise e2
java.lang.RuntimeException: java.lang.RuntimeException: Some message
By adding the exception to __cause__ (via e2.__cause__ = e1) we get an improved exception:
java.lang.RuntimeException: java.lang.RuntimeException: Some parent exception
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "/home/pelson/github/jpype/jpype/support/exception_cause.py", line 19, in <module>
raise e2
java.lang.RuntimeException: java.lang.RuntimeException: Some message
In investigating this, I also wondered if I could pass a Python exception as a cause for a Throwable, but unfortunately that wasn't possible:
>>> e1 = ValueError('foo')
>>> e2 = java.lang.RuntimeException("Some message", e1)
TypeError: No matching overloads found for constructor java.lang.RuntimeException(str,ValueError), options are:
public java.lang.RuntimeException()
public java.lang.RuntimeException(java.lang.String)
public java.lang.RuntimeException(java.lang.String,java.lang.Throwable)
public java.lang.RuntimeException(java.lang.Throwable)
I'm not sure on the practicalities, but it would be also interesting if we could make BaseException be understood as a Throwable.