4.1 Handling Python errors in Prolog

If py_call/2 or one of the other predicates that access Python causes Python to raise an exception, this exception is translated into a Prolog exception of the shape below. The library defines a rule for print_message/2 to render these errors in a human readable way.

error(python_error(ErrorType, Value, Stack), _)

Here, ErrorType is the name of the error type, as an atom, e.g., ’TypeError'. Value is the exception object represented by a Python object reference. Stack is either @none or an object that captures the Python stack. The library(janus) defines the message formatting, which makes us end up with a message like below.

?- py_call(nomodule:noattr).
ERROR: Python 'ModuleNotFoundError':
ERROR:   No module named 'nomodule'
ERROR: In:
ERROR:   [10] janus:py_call(nomodule:noattr)