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Merged
merged 3 commits into from
Nov 7, 2017
Merged

Added write only property functions for issue #1142 #1144

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0e8b028
Added write only property functions
TD22057 Oct 12, 2017
52e13f8
Updated properties to use nullptr internally
TD22057 Oct 30, 2017
086eeac
Added changelog entry
TD22057 Oct 30, 2017
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3 changes: 3 additions & 0 deletions docs/changelog.rst
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Expand Up @@ -15,6 +15,9 @@ v2.3.0 (Not yet released)
for non-MSVC compilers).
`#934 <https://github.com/pybind/pybind11/pull/934>`_.

* Added support for write only properties.
`#1144 <https://github.com/pybind/pybind11/pull/1144>`_.

v2.2.1 (September 14, 2017)
-----------------------------------------------------

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3 changes: 3 additions & 0 deletions docs/classes.rst
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Expand Up @@ -155,6 +155,9 @@ the setter and getter functions:
.def_property("name", &Pet::getName, &Pet::setName)
// ... remainder ...

Write only properties can be defined by passing ``nullptr`` as the
input for the read function.

.. seealso::

Similar functions :func:`class_::def_readwrite_static`,
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33 changes: 19 additions & 14 deletions include/pybind11/pybind11.h
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Expand Up @@ -51,6 +51,7 @@ NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
class cpp_function : public function {
public:
cpp_function() { }
cpp_function(std::nullptr_t) { }
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This is pretty minor, but I think with this nullptr constructor it would be slightly nicer to change def_property_readonly and def_property_readonly_static to pass nullptr rather than cpp_function(). It won't make any difference to how it works, but conceptually it seems nicer since the PR adds (and documents) passing a nullptr.

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Related to this: it should also be possible to specify a default-constructed cpp_function() for either the setter or getter, so perhaps add another property such as:

.def_property("impossible", py::cpp_function(), py::cpp_function())

with associated tests for attribute errors on both set or get (as per my other comment), but mainly just so we still have some test suite code invoking that code path.


/// Construct a cpp_function from a vanilla function pointer
template <typename Return, typename... Args, typename... Extra>
Expand Down Expand Up @@ -954,18 +955,18 @@ class generic_type : public object {
tinfo->get_buffer_data = get_buffer_data;
}

// rec_func must be set for either fget or fset.
void def_property_static_impl(const char *name,
handle fget, handle fset,
detail::function_record *rec_fget) {
const auto is_static = !(rec_fget->is_method && rec_fget->scope);
const auto has_doc = rec_fget->doc && pybind11::options::show_user_defined_docstrings();

detail::function_record *rec_func) {
const auto is_static = rec_func && !(rec_func->is_method && rec_func->scope);
const auto has_doc = rec_func && rec_func->doc && pybind11::options::show_user_defined_docstrings();
auto property = handle((PyObject *) (is_static ? get_internals().static_property_type
: &PyProperty_Type));
attr(name) = property(fget.ptr() ? fget : none(),
fset.ptr() ? fset : none(),
/*deleter*/none(),
pybind11::str(has_doc ? rec_fget->doc : ""));
pybind11::str(has_doc ? rec_func->doc : ""));
}
};

Expand Down Expand Up @@ -1199,7 +1200,7 @@ class class_ : public detail::generic_type {
/// Uses cpp_function's return_value_policy by default
template <typename... Extra>
class_ &def_property_readonly(const char *name, const cpp_function &fget, const Extra& ...extra) {
return def_property(name, fget, cpp_function(), extra...);
return def_property(name, fget, nullptr, extra...);
}

/// Uses return_value_policy::reference by default
Expand All @@ -1211,7 +1212,7 @@ class class_ : public detail::generic_type {
/// Uses cpp_function's return_value_policy by default
template <typename... Extra>
class_ &def_property_readonly_static(const char *name, const cpp_function &fget, const Extra& ...extra) {
return def_property_static(name, fget, cpp_function(), extra...);
return def_property_static(name, fget, nullptr, extra...);
}

/// Uses return_value_policy::reference_internal by default
Expand Down Expand Up @@ -1241,21 +1242,25 @@ class class_ : public detail::generic_type {
template <typename... Extra>
class_ &def_property_static(const char *name, const cpp_function &fget, const cpp_function &fset, const Extra& ...extra) {
auto rec_fget = get_function_record(fget), rec_fset = get_function_record(fset);
char *doc_prev = rec_fget->doc; /* 'extra' field may include a property-specific documentation string */
detail::process_attributes<Extra...>::init(extra..., rec_fget);
if (rec_fget->doc && rec_fget->doc != doc_prev) {
free(doc_prev);
rec_fget->doc = strdup(rec_fget->doc);
auto *rec_active = rec_fget;
if (rec_fget) {
char *doc_prev = rec_fget->doc; /* 'extra' field may include a property-specific documentation string */
detail::process_attributes<Extra...>::init(extra..., rec_fget);
if (rec_fget->doc && rec_fget->doc != doc_prev) {
free(doc_prev);
rec_fget->doc = strdup(rec_fget->doc);
}
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One consequence of this is that you can now do:

cl.def_property("x", nullptr, nullptr)

and get an x that can be neither read nor assigned to. I have no idea why someone would ever want to do this, but Python's property() allows it, so I suppose we can just let it slide as well:

>>> class A:
...     x = property(None, None)
... 
>>> a = A()
>>> a.x
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: unreadable attribute
>>> a.x = 2
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: can't set attribute

(So in other words, no change needed here, just an observation in passing).

}
if (rec_fset) {
doc_prev = rec_fset->doc;
char *doc_prev = rec_fset->doc;
detail::process_attributes<Extra...>::init(extra..., rec_fset);
if (rec_fset->doc && rec_fset->doc != doc_prev) {
free(doc_prev);
rec_fset->doc = strdup(rec_fset->doc);
}
if (! rec_active) rec_active = rec_fset;
}
def_property_static_impl(name, fget, fset, rec_fget);
def_property_static_impl(name, fget, fset, rec_active);
return *this;
}

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8 changes: 8 additions & 0 deletions tests/test_methods_and_attributes.cpp
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Expand Up @@ -279,12 +279,20 @@ TEST_SUBMODULE(methods_and_attributes, m) {
.def(py::init<>())
.def_readonly("def_readonly", &TestProperties::value)
.def_readwrite("def_readwrite", &TestProperties::value)
.def_property("def_writeonly", nullptr,
[](TestProperties& s,int v) { s.value = v; } )
.def_property("def_property_writeonly", nullptr, &TestProperties::set)
.def_property_readonly("def_property_readonly", &TestProperties::get)
.def_property("def_property", &TestProperties::get, &TestProperties::set)
.def_property("def_property_impossible", nullptr, nullptr)
.def_readonly_static("def_readonly_static", &TestProperties::static_value)
.def_readwrite_static("def_readwrite_static", &TestProperties::static_value)
.def_property_static("def_writeonly_static", nullptr,
[](py::object, int v) { TestProperties::static_value = v; })
.def_property_readonly_static("def_property_readonly_static",
[](py::object) { return TestProperties::static_get(); })
.def_property_static("def_property_writeonly_static", nullptr,
[](py::object, int v) { return TestProperties::static_set(v); })
.def_property_static("def_property_static",
[](py::object) { return TestProperties::static_get(); },
[](py::object, int v) { TestProperties::static_set(v); })
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44 changes: 40 additions & 4 deletions tests/test_methods_and_attributes.py
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Expand Up @@ -98,6 +98,21 @@ def test_properties():
instance.def_property = 3
assert instance.def_property == 3

with pytest.raises(AttributeError) as excinfo:
dummy = instance.def_property_writeonly # noqa: F841 unused var
assert "unreadable attribute" in str(excinfo)

instance.def_property_writeonly = 4
assert instance.def_property_readonly == 4

with pytest.raises(AttributeError) as excinfo:
dummy = instance.def_property_impossible # noqa: F841 unused var
assert "unreadable attribute" in str(excinfo)

with pytest.raises(AttributeError) as excinfo:
instance.def_property_impossible = 5
assert "can't set attribute" in str(excinfo)


def test_static_properties():
assert m.TestProperties.def_readonly_static == 1
Expand All @@ -108,13 +123,27 @@ def test_static_properties():
m.TestProperties.def_readwrite_static = 2
assert m.TestProperties.def_readwrite_static == 2

assert m.TestProperties.def_property_readonly_static == 2
with pytest.raises(AttributeError) as excinfo:
m.TestProperties.def_property_readonly_static = 3
dummy = m.TestProperties.def_writeonly_static # noqa: F841 unused var
assert "unreadable attribute" in str(excinfo)

m.TestProperties.def_writeonly_static = 3
assert m.TestProperties.def_readonly_static == 3

assert m.TestProperties.def_property_readonly_static == 3
with pytest.raises(AttributeError) as excinfo:
m.TestProperties.def_property_readonly_static = 99
assert "can't set attribute" in str(excinfo)

m.TestProperties.def_property_static = 3
assert m.TestProperties.def_property_static == 3
m.TestProperties.def_property_static = 4
assert m.TestProperties.def_property_static == 4

with pytest.raises(AttributeError) as excinfo:
dummy = m.TestProperties.def_property_writeonly_static
assert "unreadable attribute" in str(excinfo)

m.TestProperties.def_property_writeonly_static = 5
assert m.TestProperties.def_property_static == 5

# Static property read and write via instance
instance = m.TestProperties()
Expand All @@ -127,6 +156,13 @@ def test_static_properties():
assert m.TestProperties.def_readwrite_static == 2
assert instance.def_readwrite_static == 2

with pytest.raises(AttributeError) as excinfo:
dummy = instance.def_property_writeonly_static # noqa: F841 unused var
assert "unreadable attribute" in str(excinfo)

instance.def_property_writeonly_static = 4
assert instance.def_property_static == 4

# It should be possible to override properties in derived classes
assert m.TestPropertiesOverride().def_readonly == 99
assert m.TestPropertiesOverride.def_readonly_static == 99
Expand Down