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Add py::object casting example to embedding docs #2466

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Sep 9, 2020
Merged

Add py::object casting example to embedding docs #2466

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a3b0971
Add py::object casting example to embedding docs
kohr-h Sep 6, 2020
8982c1a
Move implicit cast example to object.rst
kohr-h Sep 6, 2020
250ed51
Move to bottom and improve implicit casting text
kohr-h Sep 7, 2020
b907678
Fix xref
kohr-h Sep 7, 2020
b4c0df3
Improve wording as per @bstaletic's suggestion
kohr-h Sep 8, 2020
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19 changes: 19 additions & 0 deletions docs/advanced/embedding.rst
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Expand Up @@ -105,6 +105,25 @@ The two approaches can also be combined:
std::cout << message;
}

Typically, a call to a function in a `py::module` returns a generic `py::object`,
which can often be autmatically cast to a specialized pybind11 type:
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Calling py::module::import returns a py::module.

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That's why I wrote "typically" 😉
But maybe that's not true either. Is it?

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It is true, at least from my reading:

pybind11/include/pybind11/pybind11.h

Line 914 in 37f845a

static module import(const char *name) {

I think the "typically" can be dropped, because in C++, it is py::module (the C++ type itself).


.. code-block:: cpp

py::module os = py::module::import("os");
py::module path = py::module::import("os.path"); // like 'import os.path as path'
py::module np = py::module::import("numpy"); // like 'import numpy as np'

py::str curdir_abs = path.attr("abspath")(path.attr("curdir"));
py::print(py::str("Current directory: ") + curdir_abs);
py::dict environ = os.attr("environ");
py::print(environ["HOME"]);
py::array_t<float> arr = np.attr("ones")(3, "dtype"_a="float32");
py::print(py::repr(arr + py::int_(1)));

(Note that this example requires ``#include <pybind11/numpy.h>`` and
``using namespace pybind11::literals;`` to work.)

Importing modules
=================

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