You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
57 lines
2.0 KiB
57 lines
2.0 KiB
Utilities
|
|
#########
|
|
|
|
Using Python's print function in C++
|
|
====================================
|
|
|
|
The usual way to write output in C++ is using ``std::cout`` while in Python one
|
|
would use ``print``. Since these methods use different buffers, mixing them can
|
|
lead to output order issues. To resolve this, pybind11 modules can use the
|
|
:func:`py::print` function which writes to Python's ``sys.stdout`` for consistency.
|
|
|
|
Python's ``print`` function is replicated in the C++ API including optional
|
|
keyword arguments ``sep``, ``end``, ``file``, ``flush``. Everything works as
|
|
expected in Python:
|
|
|
|
.. code-block:: cpp
|
|
|
|
py::print(1, 2.0, "three"); // 1 2.0 three
|
|
py::print(1, 2.0, "three", "sep"_a="-"); // 1-2.0-three
|
|
|
|
auto args = py::make_tuple("unpacked", true);
|
|
py::print("->", *args, "end"_a="<-"); // -> unpacked True <-
|
|
|
|
Evaluating Python expressions from strings and files
|
|
====================================================
|
|
|
|
pybind11 provides the :func:`eval` and :func:`eval_file` functions to evaluate
|
|
Python expressions and statements. The following example illustrates how they
|
|
can be used.
|
|
|
|
Both functions accept a template parameter that describes how the argument
|
|
should be interpreted. Possible choices include ``eval_expr`` (isolated
|
|
expression), ``eval_single_statement`` (a single statement, return value is
|
|
always ``none``), and ``eval_statements`` (sequence of statements, return value
|
|
is always ``none``).
|
|
|
|
.. code-block:: cpp
|
|
|
|
// At beginning of file
|
|
#include <pybind11/eval.h>
|
|
|
|
...
|
|
|
|
// Evaluate in scope of main module
|
|
py::object scope = py::module::import("__main__").attr("__dict__");
|
|
|
|
// Evaluate an isolated expression
|
|
int result = py::eval("my_variable + 10", scope).cast<int>();
|
|
|
|
// Evaluate a sequence of statements
|
|
py::eval<py::eval_statements>(
|
|
"print('Hello')\n"
|
|
"print('world!');",
|
|
scope);
|
|
|
|
// Evaluate the statements in an separate Python file on disk
|
|
py::eval_file("script.py", scope);
|