Expose enum_ entries as new "members" attribute #666

mdcb · 2017-02-13T23:12:28Z

Brings convenience of being able to list the entries making an Enum. Side effect simplifies the .export_values() implementation.

jagerman · 2017-02-14T06:10:34Z

I didn't look at this in great detail, but a couple comments:

I wonder if __members__ would be a more appropriate choice for the name?
Judging from the travis output, there appears to be an issue with your code under Python 2.7. (You can ignore the PYTHON=3.5 GCC=6/7 failures, they are known issues).

mdcb · 2017-02-14T19:49:00Z

I eventually chose '__items__'
Update should fix the 2.7 issue.

wjakob · 2017-02-26T22:09:55Z

include/pybind11/pybind11.h

@@ -1407,12 +1407,13 @@ template <typename Type> class enum_ : public class_<Type> {
            !std::is_same<detail::first_of_t<arithmetic_tag, void, Extra...>,
                          void>::value;

-        auto entries = new std::unordered_map<Scalar, const char *>();
+        auto entries = new pybind11::dict();


use of new here is problematic (this will never be cleaned up.) Better to use standard python objects and rely on reference counting.

wjakob · 2017-02-26T22:10:12Z

include/pybind11/pybind11.h

    }

    /// Export enumeration entries into the parent scope
    enum_ &export_values() {
-#if !defined(PYPY_VERSION)


neat! That's a nice simplification.

wjakob · 2017-02-26T22:12:56Z

^@aldanor

Generally switching from the C++ map to dict is nice. With regards to the precise conventions (e.g. __items__, __members__, etc. Or perhaps just a type implementing the iterator interface?), I am wondering: is there a pythonic answer? Potentially related: #530.

llchan · 2017-02-27T18:15:57Z

I'm a proponent of keeping it as close to the PEP 435 enums as possible, i.e. with __members__ and an iterator interface. Technically it's supposed to be in definition order too, how do we feel about using an OrderedDict for it? If we dont support <2.7 it should be pretty straightforward.

wjakob · 2017-02-27T18:17:46Z

We always support 2.7 :)

mdcb · 2017-02-27T18:34:59Z

Lastest push fixes conflict issue and use __members__.
Trivial replacement of new pointer with pybind11:dict m_entries

        def("__repr__", [name, this](Type value) -> std::string {
            for (const auto &kv : this->m_entries) {
                if (kv.second.cast<Type>() == value)
                    return std::string(name) + "." + kv.first.cast<std::string>();
            }
            return std::string(name) + ".???";
        });

gives:

error: expected primary-expression before ‘>’ token
                 if (kv.second.cast<Type>() == value)

Looking into that and the iterator aspects. Anyone wishing to jump in welcomed.

llchan · 2017-02-27T18:51:36Z

@wjakob Maybe my "<2.7" notation wasnt very clear. I just mean that if we don't care about supporting 2.6 and below, we can assume OrderedDict is available and not worry about fallback mechanisms.

@mdcb maybe you need kv.second.template cast<Type>()?

llchan · 2017-02-27T18:55:58Z

Btw, the __iter__ in the CPython/enum34 enums do this:

def __iter__(cls):
    return (cls._member_map_[name] for name in cls._member_names_)

We could probably do the equivalent with m_entries.

Also I think we should follow their lead and make __members__ a property that returns a copy of m_entries, otherwise the user can mutate that dict.

@property
def __members__(cls):
    return cls._member_map_.copy()

mdcb · 2017-03-01T20:43:32Z

Latest push should address the 'new' issue, readonly property, copy on access. Looked briefly at the iterator protocol - that might have to come from someone else and/or different PR.
PS: waiting for CI results to squash the 2 commits.

jagerman · 2017-03-02T02:02:56Z

travis-ci is having some technical problems tonight, so you'll probably have to wait a bit to get a successful build.

jagerman · 2017-03-03T15:31:26Z

include/pybind11/pybind11.h

+                    return std::string(name) + "." + kv.first.PREFIX_MEMBER_TEMPLATE cast<std::string>();
+            }
+            return std::string(name) + ".???";
+#undef PREFIX_MEMBER_TEMPLATE


I think you can simply this whole block (and get rid of the ugly MSVC workaround macro) as:

def("__repr__", [name, m_entries_ptr](Type value) -> str { for (const auto &kv : reinterpret_borrow<dict>(m_entries_ptr)) { if (pybind11::cast<Type>(kv.second) == value) return str("{}.{}").format(name, kv.first); } return str("{}.???").format(name); });

jagerman · 2017-03-03T15:42:10Z

Re: iterator interface: I don't think it is worthwhile. The main issue is that the iterator interface has to be added on the metatype, not the type itself (because iteration is on EnumType, not EnumType()). To support that, we'd have to stop inheriting from py::class_ and instead add a new metatype for enums (which is what Python itself does). That's a whole lot of work for very little gain. Better, I think, to accept this as is, and eventually just use Python's enum metatype (i.e. as proposed in #530) on Python 3.4+, with the current class_ wrapper providing an incomplete API fallback for < 3.4.

Aside from the __repr__ simplification I commented on, I think this is good to go.

llchan · 2017-03-03T16:08:15Z

Oh derp, you're totally right, I just Ctrl-F'd the __iter__ without looking at what (meta)class it's in. The __members__ field is sufficient to at least extract that information, so I agree we can table the iterator interface for now.

mdcb · 2017-03-03T16:08:29Z

@jagerman - squashed your __repr__ in lastest push

jagerman · 2017-03-03T16:40:46Z

Assuming the WIP build succeeds, no need to squash (I can do that when merging).

mdcb · 2017-03-03T16:41:47Z

Ok - note ther typo in docs.

jagerman · 2017-03-03T16:44:07Z

Ah, well that needs a commit to fix it.

… a copy.

mdcb · 2017-03-03T16:47:20Z

shake and bake

jagerman · 2017-03-03T18:17:28Z

Merged, thanks!

mdcb · 2017-03-04T01:05:27Z

include/pybind11/pybind11.h

+            for (const auto &kv : reinterpret_borrow<dict>(m_entries_ptr))
+                m[kv.first] = kv.second;
+            return m;
+        }, return_value_policy::copy);
        def("__init__", [](Type& value, Scalar i) { value = (Type)i; });
        def("__init__", [](Type& value, Scalar i) { new (&value) Type((Type) i); });


unrelated to this PR but highlighted by the diff, lines 1145 / 1146 look odd.

jagerman · 2017-03-04T14:09:42Z

Can you clarify "odd"?

jagerman · 2017-03-04T14:16:40Z

Oh, you mean two identical constructors declared. Yes, that does look strange.

mdcb changed the title ~~Expose enum_ entries as new "entries" attribute~~ Expose enum_ entries as new "__items__" attribute Feb 14, 2017

wjakob reviewed Feb 26, 2017

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mdcb changed the title ~~Expose enum_ entries as new "__items__" attribute~~ Expose enum_ entries as new "__members__" attribute Feb 27, 2017

jagerman reviewed Mar 3, 2017

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Expose enum_ entries as "__members__" read-only property. Getters get…

af936e1

… a copy.

jagerman merged commit 414ee16 into pybind:master Mar 3, 2017

mdcb commented Mar 4, 2017

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jagerman modified the milestone: v2.1 Mar 19, 2017

jagerman mentioned this pull request Apr 6, 2017

WIP: Python 3 enums #781

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FWD pybind11 google/pybind11clif#666

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Expose enum_ entries as new "members" attribute #666

Expose enum_ entries as new "members" attribute #666

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Expose enum_ entries as new "__members__" attribute #666

Expose enum_ entries as new "__members__" attribute #666

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Expose enum_ entries as new "members" attribute #666

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