Exception Handling

Since Jep 3.3

Uncaught Exceptions

The Jep interpreter frequently checks for exceptions to prevent the native code from getting in a bad state. When an uncaught exception is encountered:

1. Jep creates a new JepException. If the exception was a Java exception, the cause will be the original Java exception.
2. Jep attempts to use the traceback module to build a stack trace of the Python code. If successful, it will use the Python traceback information to emulate Java StackTraceElements for a more complete picture of the trace to the error.
3. Jep will then throw the JepException out of the interpreter back to the calling Java code.

Prior to Jep 3.3, Jep would throw a JepException but not include stacktrace/traceback information.

Catching Java exceptions in Python

If Java code invoked from Python throws an exception of one of a few select types, you can catch the exception in Python if desired. For example:

try:
   # throws ClassNotFoundException
   from java.lang import ArrayList
except ImportError as ie:
   from java.util import ArrayList

The Java types that support this with their equivalent Python exceptions are:

• ClassNotFoundException -> ImportError
• IndexOutOfBoundsException -> IndexError
• IOException -> IOError
• ClassCastException -> TypeError
• IllegalArgumentException -> ValueError
• ArithmeticException -> ArithmeticError
• OutOfMemoryError -> MemoryError
• AssertionError -> AssertionError

All other Java exceptions will be treated by the Jep interpreter as RuntimeErrors.