/** Copyright (c) 2014 Alex Tsui Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. */ #include #include #include "ParseHelper.h" #include "ParseListener.h" /** Demonstrates the ParseHelper. Call it with some of the python files in data/. */ int main( int argc, char *argv[] ) { if ( argc < 2 ) { std::cout << "Usage: " << argv[0] << " file\n"; return 1; } ParseHelper helper; helper.subscribe( new EchoListener ); std::ifstream ifs( argv[1] ); while ( ! ifs.eof( ) ) { std::string str; std::getline( ifs, str ); helper.process( str ); } return 0; } eecommitdiffstats
path: root/3rdparty/pybind11/docs/advanced/pycpp/object.rst
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Python types
############

.. _wrappers:

Available wrappers
==================

All major Python types are available as thin C++ wrapper classes. These
can also be used as function parameters -- see :ref:`python_objects_as_args`.

Available types include :class:`handle`, :class:`object`, :class:`bool_`,
:class:`int_`, :class:`float_`, :class:`str`, :class:`bytes`, :class:`tuple`,
:class:`list`, :class:`dict`, :class:`slice`, :class:`none`, :class:`capsule`,
:class:`iterable`, :class:`iterator`, :class:`function`, :class:`buffer`,
:class:`array`, and :class:`array_t`.

.. warning::

    Be sure to review the :ref:`pytypes_gotchas` before using this heavily in
    your C++ API.

.. _casting_back_and_forth:

Casting back and forth
======================

In this kind of mixed code, it is often necessary to convert arbitrary C++
types to Python, which can be done using :func:`py::cast`:

.. code-block:: cpp

    MyClass *cls = ..;
    py::object obj = py::cast(cls);

The reverse direction uses the following syntax:

.. code-block:: cpp

    py::object obj = ...;
    MyClass *cls = obj.cast<MyClass *>();

When conversion fails, both directions throw the exception :class:`cast_error`.

.. _python_libs:

Accessing Python libraries from C++
===================================

It is also possible to import objects defined in the Python standard
library or available in the current Python environment (``sys.path``) and work
with these in C++.

This example obtains a reference to the Python ``Decimal`` class.

.. code-block:: cpp

    // Equivalent to "from decimal import Decimal"
    py::object Decimal = py::module_::import("decimal").attr("Decimal");

.. code-block:: cpp

    // Try to import scipy
    py::object scipy = py::module_::import("scipy");
    return scipy.attr("__version__");


.. _calling_python_functions:

Calling Python functions
========================

It is also possible to call Python classes, functions and methods
via ``operator()``.

.. code-block:: cpp

    // Construct a Python object of class Decimal
    py::object pi = Decimal("3.14159");

.. code-block:: cpp

    // Use Python to make our directories
    py::object os = py::module_::import("os");
    py::object makedirs = os.attr("makedirs");
    makedirs("/tmp/path/to/somewhere");

One can convert the result obtained from Python to a pure C++ version
if a ``py::class_`` or type conversion is defined.

.. code-block:: cpp

    py::function f = <...>;
    py::object result_py = f(1234, "hello", some_instance);
    MyClass &result = result_py.cast<MyClass>();

.. _calling_python_methods:

Calling Python methods
========================

To call an object's method, one can again use ``.attr`` to obtain access to the
Python method.

.. code-block:: cpp

    // Calculate e^π in decimal
    py::object exp_pi = pi.attr("exp")();
    py::print(py::str(exp_pi));

In the example above ``pi.attr("exp")`` is a *bound method*: it will always call
the method for that same instance of the class. Alternately one can create an
*unbound method* via the Python class (instead of instance) and pass the ``self``
object explicitly, followed by other arguments.

.. code-block:: cpp

    py::object decimal_exp = Decimal.attr("exp");

    // Compute the e^n for n=0..4
    for (int n = 0; n < 5; n++) {
        py::print(decimal_exp(Decimal(n));
    }

Keyword arguments
=================

Keyword arguments are also supported. In Python, there is the usual call syntax:

.. code-block:: python