Implicit conversion from Null when inside a vector

[afryt]

Can't make an implicit conversion from None (py::none or py::object) to my class work.
It is the same issue as #642 but I'd like to provide a non-obscure use case.

In the interface I'm writing I'd like to provide a constructor from a Python list. The elements of the list can be double, string and None (ideally). The constructor being exposed is this one:
A::A(const vector<B>& l)
I expose it using

py::class_<A> m(module, "A");
m.def(py::init<vector<B>>&>())

I'd like to call this using:

A([None, 1.0, "string"])

I registered implicit conversion from double and string to B and it flies, that is I can create object A using A([1.0, 'string']). This works because B has implicit conversions:
B.def(py::init<double>()).def(py::init<std::string>()).def(py::init<>());
and a list of py::implicitly_convertible<double, B>()....

Question: How to I add implicit conversion from Python None to use B() when in a list?

[tboyce021]

I'm running into this same issue with a map. Did you ever figure out a workaround?

[afryt]

No, unfortunately I haven't. If you come up with something please share.

[bstaletic]

b_class.def("__init__" [](py::object o) {
    if (o.is_none()) return B{};
    else throw py::type_error("boom");
});

If this doesn't solve it, feel free to reopen the issue.

[YannickJadoul]

Or #include <pybind11/stl.h> + std::optional<...>.