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Add make_namespace function and tests
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Jouke Witteveen authored and joukewitteveen committed Aug 22, 2021
1 parent 4f29b8a commit fce90ef
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42 changes: 41 additions & 1 deletion docs/advanced/pycpp/object.rst
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Expand Up @@ -20,6 +20,46 @@ Available types include :class:`handle`, :class:`object`, :class:`bool_`,
Be sure to review the :ref:`pytypes_gotchas` before using this heavily in
your C++ API.

.. _instantiating_compound_types:

Instantiating compound Python types from C++
============================================

Dictionaries can be initialized in the :class:`dict` constructor:

.. code-block:: cpp
using namespace pybind11::literals; // to bring in the `_a` literal
py::dict d("spam"_a=py::none(), "eggs"_a=42);
A tuple of python objects can be instantiated using :func:`py::make_tuple`:

.. code-block:: cpp
py::tuple tup = py::make_tuple(42, py::none(), "spam");
Each element is converted to a supported Python type.

A `simple namespace`_ can be instantiated using :func:`py::make_namespace`:

.. code-block:: cpp
using namespace pybind11::literals; // to bring in the `_a` literal
py::object ns = py::make_namespace("spam"_a=py::none(), "eggs"_a=42);
Attributes on a namespace can be modified with the :func:`py::delattr`,
:func:`py::getattr`, and :func:`py::setattr` functions. Namespaces can be useful
as lightweight stand-ins for class instances.

.. note::

``make_namespace`` is not available in Python 2.

.. versionchanged:: 2.8
``make_namespace`` added.

.. _simple namespace: https://docs.python.org/3/library/types.html#types.SimpleNamespace

.. _casting_back_and_forth:

Casting back and forth
Expand All @@ -30,7 +70,7 @@ types to Python, which can be done using :func:`py::cast`:

.. code-block:: cpp
MyClass *cls = ..;
MyClass *cls = ...;
py::object obj = py::cast(cls);
The reverse direction uses the following syntax:
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10 changes: 10 additions & 0 deletions include/pybind11/cast.h
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Expand Up @@ -1018,6 +1018,16 @@ template <return_value_policy policy = return_value_policy::automatic_reference,
return result;
}

#if PY_VERSION_HEX >= 0x03030000
template <typename... Args,
typename = detail::enable_if_t<args_are_all_keyword_or_ds<Args...>()>>
object make_namespace(Args&&... args_) {
PyObject *ns = _PyNamespace_New(dict(std::forward<Args>(args_)...).ptr());
if (!ns) throw error_already_set();
return reinterpret_steal<object>(ns);
}
#endif

/// \ingroup annotations
/// Annotation for arguments
struct arg {
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13 changes: 13 additions & 0 deletions tests/test_pytypes.cpp
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Expand Up @@ -70,6 +70,19 @@ TEST_SUBMODULE(pytypes, m) {
m.def("dict_contains",
[](const py::dict &dict, const char *val) { return dict.contains(val); });

// test_tuple
m.def("get_tuple", []() { return py::make_tuple(42, py::none(), "spam"); });

#if PY_VERSION_HEX >= 0x03030000
// test_namespace
m.def("get_namespace", []() {
auto ns = py::make_namespace("attr"_a=42, "x"_a="foo", "wrong"_a=1);
py::delattr(ns, "wrong");
py::setattr(ns, "right", py::int_(2));
return ns;
});
#endif

// test_str
m.def("str_from_string", []() { return py::str(std::string("baz")); });
m.def("str_from_bytes", []() { return py::str(py::bytes("boo", 3)); });
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13 changes: 13 additions & 0 deletions tests/test_pytypes.py
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Expand Up @@ -99,6 +99,19 @@ def test_dict(capture, doc):
assert m.dict_keyword_constructor() == {"x": 1, "y": 2, "z": 3}


def test_tuple():
assert m.get_tuple() == (42, None, "spam")


@pytest.mark.skipif("env.PY2")
def test_namespace():
ns = m.get_namespace()
assert ns.attr == 42
assert ns.x == "foo"
assert ns.right == 2
assert not hasattr(ns, "wrong")


def test_str(doc):
assert m.str_from_string().encode().decode() == "baz"
assert m.str_from_bytes().encode().decode() == "boo"
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