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.

Note: 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.