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+Exceptions
+##########
+
+Built-in exception translation
+==============================
+
+When C++ code invoked from Python throws an ``std::exception``, it is
+automatically converted into a Python ``Exception``. pybind11 defines multiple
+special exception classes that will map to different types of Python
+exceptions:
+
+.. tabularcolumns:: |p{0.5\textwidth}|p{0.45\textwidth}|
+
++--------------------------------------+--------------------------------------+
+| C++ exception type | Python exception type |
++======================================+======================================+
+| :class:`std::exception` | ``RuntimeError`` |
++--------------------------------------+--------------------------------------+
+| :class:`std::bad_alloc` | ``MemoryError`` |
++--------------------------------------+--------------------------------------+
+| :class:`std::domain_error` | ``ValueError`` |
++--------------------------------------+--------------------------------------+
+| :class:`std::invalid_argument` | ``ValueError`` |
++--------------------------------------+--------------------------------------+
+| :class:`std::length_error` | ``ValueError`` |
++--------------------------------------+--------------------------------------+
+| :class:`std::out_of_range` | ``IndexError`` |
++--------------------------------------+--------------------------------------+
+| :class:`std::range_error` | ``ValueError`` |
++--------------------------------------+--------------------------------------+
+| :class:`std::overflow_error` | ``OverflowError`` |
++--------------------------------------+--------------------------------------+
+| :class:`pybind11::stop_iteration` | ``StopIteration`` (used to implement |
+| | custom iterators) |
++--------------------------------------+--------------------------------------+
+| :class:`pybind11::index_error` | ``IndexError`` (used to indicate out |
+| | of bounds access in ``__getitem__``, |
+| | ``__setitem__``, etc.) |
++--------------------------------------+--------------------------------------+
+| :class:`pybind11::value_error` | ``ValueError`` (used to indicate |
+| | wrong value passed in |
+| | ``container.remove(...)``) |
++--------------------------------------+--------------------------------------+
+| :class:`pybind11::key_error` | ``KeyError`` (used to indicate out |
+| | of bounds access in ``__getitem__``, |
+| | ``__setitem__`` in dict-like |
+| | objects, etc.) |
++--------------------------------------+--------------------------------------+
+| :class:`pybind11::error_already_set` | Indicates that the Python exception |
+| | flag has already been set via Python |
+| | API calls from C++ code; this C++ |
+| | exception is used to propagate such |
+| | a Python exception back to Python. |
++--------------------------------------+--------------------------------------+
+
+When a Python function invoked from C++ throws an exception, it is converted
+into a C++ exception of type :class:`error_already_set` whose string payload
+contains a textual summary.
+
+There is also a special exception :class:`cast_error` that is thrown by
+:func:`handle::call` when the input arguments cannot be converted to Python
+objects.
+
+Registering custom translators
+==============================
+
+If the default exception conversion policy described above is insufficient,
+pybind11 also provides support for registering custom exception translators.
+To register a simple exception conversion that translates a C++ exception into
+a new Python exception using the C++ exception's ``what()`` method, a helper
+function is available:
+
+.. code-block:: cpp
+
+ py::register_exception<CppExp>(module, "PyExp");
+
+This call creates a Python exception class with the name ``PyExp`` in the given
+module and automatically converts any encountered exceptions of type ``CppExp``
+into Python exceptions of type ``PyExp``.
+
+When more advanced exception translation is needed, the function
+``py::register_exception_translator(translator)`` can be used to register
+functions that can translate arbitrary exception types (and which may include
+additional logic to do so). The function takes a stateless callable (e.g. a
+function pointer or a lambda function without captured variables) with the call
+signature ``void(std::exception_ptr)``.
+
+When a C++ exception is thrown, the registered exception translators are tried
+in reverse order of registration (i.e. the last registered translator gets the
+first shot at handling the exception).
+
+Inside the translator, ``std::rethrow_exception`` should be used within
+a try block to re-throw the exception. One or more catch clauses to catch
+the appropriate exceptions should then be used with each clause using
+``PyErr_SetString`` to set a Python exception or ``ex(string)`` to set
+the python exception to a custom exception type (see below).
+
+To declare a custom Python exception type, declare a ``py::exception`` variable
+and use this in the associated exception translator (note: it is often useful
+to make this a static declaration when using it inside a lambda expression
+without requiring capturing).
+
+
+The following example demonstrates this for a hypothetical exception classes
+``MyCustomException`` and ``OtherException``: the first is translated to a
+custom python exception ``MyCustomError``, while the second is translated to a
+standard python RuntimeError:
+
+.. code-block:: cpp
+
+ static py::exception<MyCustomException> exc(m, "MyCustomError");
+ py::register_exception_translator([](std::exception_ptr p) {
+ try {
+ if (p) std::rethrow_exception(p);
+ } catch (const MyCustomException &e) {
+ exc(e.what());
+ } catch (const OtherException &e) {
+ PyErr_SetString(PyExc_RuntimeError, e.what());
+ }
+ });
+
+Multiple exceptions can be handled by a single translator, as shown in the
+example above. If the exception is not caught by the current translator, the
+previously registered one gets a chance.
+
+If none of the registered exception translators is able to handle the
+exception, it is handled by the default converter as described in the previous
+section.
+
+.. seealso::
+
+ The file :file:`tests/test_exceptions.cpp` contains examples
+ of various custom exception translators and custom exception types.
+
+.. note::
+
+ You must call either ``PyErr_SetString`` or a custom exception's call
+ operator (``exc(string)``) for every exception caught in a custom exception
+ translator. Failure to do so will cause Python to crash with ``SystemError:
+ error return without exception set``.
+
+ Exceptions that you do not plan to handle should simply not be caught, or
+ may be explicitly (re-)thrown to delegate it to the other,
+ previously-declared existing exception translators.