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36 * \brief Exception translation.
38 * Note that C++ exception objects are not actually bound to Python objects
39 * because C++ cannot give ownership of a thrown exception to the interpreter.
40 * Instead, we catch C++ exceptions and translate them into Python exceptions.
42 * As of pybind11 2.2, pybind does not provide a way to automatically express
43 * C++ exception class inheritance to Python, and only supports simple Python
44 * exceptions initialized with strings at the time of translation. (Automatic
45 * translation uses `std::exception::what()`)
47 * Currently, we restrict ourselves to this simple translation. Future versions
48 * may use the Python C API directly to support richer exception classes.
50 * \todo Determine inheritance relationship or equality between
51 * gmxapi._gmxapi.Exception and gmxapi.exceptions.Error, if any.
53 * \author M. Eric Irrgang <ericirrgang@gmail.com>
55 * \ingroup module_python
57 #include "gmxapi/exceptions.h"
68 namespace py = pybind11;
71 void export_exceptions(pybind11::module& m)
73 // These two lines could cause exceptions, but they are already handled,
74 // causing an ImportError for the _gmxapi submodule raised from the
75 // ImportError or AttributeError that caused the failure.
76 // If we find that this is too cryptic or that there are too many places
77 // that import could fail, we can use the Python C API directly
78 // (in the module.cpp code block preceded by the PYBIND11 macro) to set a
79 // new PyExc_ImportError manually and return a nullptr immediately.
80 const auto packageModule = py::module::import("gmxapi");
81 const auto gmxapi_exceptions_error = packageModule.attr("exceptions").attr("Error");
83 static py::exception<gmxapi::Exception> baseException(m, "Exception", gmxapi_exceptions_error.ptr());
85 // Developer note: as of pybind11 2.2.4, the py::exception template argument
86 // is unused internally, but required.
87 struct UnknownExceptionPlaceHolder
90 static py::exception<UnknownExceptionPlaceHolder> unknownException(m, "UnknownException",
92 unknownException.doc() =
93 "GROMACS library produced an exception that is "
94 "not mapped in gmxapi or which should have been "
95 "caught at a lower level. I.e. a bug. (Please report.)";
97 // Catch unexpected/unbound exceptions from libgromacs or libgmxapi.
98 py::register_exception_translator([](std::exception_ptr p) {
103 std::rethrow_exception(p);
106 catch (const gmxapi::Exception& e)
108 // Nothing should be throwing the base exception and all gmxapi
109 // exceptions should be mapped in this module. Differences
110 // between GROMACS version and Python package version could leave
111 // some exceptions unmapped, but we should add an alert in case
112 // an exception gets overlooked.
113 std::string message = "Generic gmxapi exception caught: ";
115 baseException(message.c_str());
117 catch (const std::exception& e)
119 std::string message = "Please report GROMACS bug. Unhandled C++ exception: ";
121 unknownException(message.c_str());
125 // Map gmxapi exceptions from gmxapi/exceptions.h to Python package exceptions.
126 // Note: C++ exception translation occurs in revers order of registration,
127 // So derived exceptions must be registered after their base exceptions.
128 // TODO: We could have more informative exception class docstrings
129 // by linking to online docs or if we had a way to reuse doxygen docs.
133 py::register_exception<gmxapi::ProtocolError>(m, "ProtocolError", baseException.ptr());
134 exception.doc() = "Behavioral protocol violated.";
138 auto exception = py::register_exception<gmxapi::NotImplementedError>(
139 m, "NotImplementedError", baseException.ptr());
140 exception.doc() = "Expected feature is not implemented.";
145 py::register_exception<gmxapi::UsageError>(m, "UsageError", baseException.ptr());
146 exception.doc() = "Unacceptable API usage.";
151 } // namespace detail
153 } // end namespace gmxpy