Access Python Exception object

[espositofulvio]

Issue description

When catching a Python exception from C++, there is no way to access the exception data. Python exceptions are converted to error_already_set, but its members are private and there's no way to access the actual exception data in case the value member is set as for StopIteration.

[DenisSalem]

Same issue here. Well, it's more like a missing feature than an issue, but still.

Regards.

[bstaletic]

There's currently a pull request that provides getters for the private members.

[DenisSalem]

@bstaletic if your refer to this #1641, it only allows the user to read type, value and trace private members. There is no way as far as I know to bind C++ exception class attributes to the newly created python exception, like you would do with def_readwrite.

[YannickJadoul]

Now that error_already_set has value() and type() are there, after #1641, you should be able to query these:

        try {
                py::exec("raise ValueError(42)");
        }
        catch (const py::error_already_set &e) {
                py::print(e.value().attr("args"));
        }

This nicely prints a tuple (42,).

There is no way as far as I know to bind C++ exception class attributes

No, because py::error_already_set is an wrapper around a Python exception.

bind C++ exception class attributes to the newly created python exception, like you would do with def_readwrite.

If you mean adding methods and properties to the custom C++ exceptions exposed to Python, that is a long standing feature request (can't immediately fine one, but I'm sure there's one or more issues), but far from easy to implement. But it doesn't seem like that's @espositofulvio's original question?

[espositofulvio]

Hi @YannickJadoul,
my question is fully addressed by this change. Thanks a lot!

[YannickJadoul]

Great! Thanks for confirming! :-)