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authorJason Lowe-Power <jason@lowepower.com>2017-11-17 17:02:05 -0800
committerJason Lowe-Power <jason@lowepower.com>2017-12-14 00:27:59 +0000
commitf07d5069d86e31ecf195664850f79fb00c445bd3 (patch)
treef54ac06896fa828f873d199a0e9b25bd94911c79 /ext/pybind11/docs/advanced/pycpp/utilities.rst
parent3f64b374c49491f18dc2ca538ed8c8597e4aac83 (diff)
downloadgem5-f07d5069d86e31ecf195664850f79fb00c445bd3.tar.xz
ext: Upgrade PyBind11 to version 2.2.1
This upgrade is necessary for pybind to build with GCC 7.2. We still need to add the patch for stl.h. MSC_FULL_VER change is no longer needed. See https://gem5-review.googlesource.com/c/public/gem5/+/2230 Change-Id: I806729217d022070583994c2dfcaa74476aef30f Signed-off-by: Jason Lowe-Power <jason@lowepower.com> Reviewed-on: https://gem5-review.googlesource.com/5801 Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com> Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Diffstat (limited to 'ext/pybind11/docs/advanced/pycpp/utilities.rst')
-rw-r--r--ext/pybind11/docs/advanced/pycpp/utilities.rst103
1 files changed, 95 insertions, 8 deletions
diff --git a/ext/pybind11/docs/advanced/pycpp/utilities.rst b/ext/pybind11/docs/advanced/pycpp/utilities.rst
index ba0dbef88..369e7c94d 100644
--- a/ext/pybind11/docs/advanced/pycpp/utilities.rst
+++ b/ext/pybind11/docs/advanced/pycpp/utilities.rst
@@ -21,19 +21,81 @@ expected in Python:
auto args = py::make_tuple("unpacked", true);
py::print("->", *args, "end"_a="<-"); // -> unpacked True <-
+.. _ostream_redirect:
+
+Capturing standard output from ostream
+======================================
+
+Often, a library will use the streams ``std::cout`` and ``std::cerr`` to print,
+but this does not play well with Python's standard ``sys.stdout`` and ``sys.stderr``
+redirection. Replacing a library's printing with `py::print <print>` may not
+be feasible. This can be fixed using a guard around the library function that
+redirects output to the corresponding Python streams:
+
+.. code-block:: cpp
+
+ #include <pybind11/iostream.h>
+
+ ...
+
+ // Add a scoped redirect for your noisy code
+ m.def("noisy_func", []() {
+ py::scoped_ostream_redirect stream(
+ std::cout, // std::ostream&
+ py::module::import("sys").attr("stdout") // Python output
+ );
+ call_noisy_func();
+ });
+
+This method respects flushes on the output streams and will flush if needed
+when the scoped guard is destroyed. This allows the output to be redirected in
+real time, such as to a Jupyter notebook. The two arguments, the C++ stream and
+the Python output, are optional, and default to standard output if not given. An
+extra type, `py::scoped_estream_redirect <scoped_estream_redirect>`, is identical
+except for defaulting to ``std::cerr`` and ``sys.stderr``; this can be useful with
+`py::call_guard`, which allows multiple items, but uses the default constructor:
+
+.. code-block:: py
+
+ // Alternative: Call single function using call guard
+ m.def("noisy_func", &call_noisy_function,
+ py::call_guard<py::scoped_ostream_redirect,
+ py::scoped_estream_redirect>());
+
+The redirection can also be done in Python with the addition of a context
+manager, using the `py::add_ostream_redirect() <add_ostream_redirect>` function:
+
+.. code-block:: cpp
+
+ py::add_ostream_redirect(m, "ostream_redirect");
+
+The name in Python defaults to ``ostream_redirect`` if no name is passed. This
+creates the following context manager in Python:
+
+.. code-block:: python
+
+ with ostream_redirect(stdout=True, stderr=True):
+ noisy_function()
+
+It defaults to redirecting both streams, though you can use the keyword
+arguments to disable one of the streams if needed.
+
+.. note::
+
+ The above methods will not redirect C-level output to file descriptors, such
+ as ``fprintf``. For those cases, you'll need to redirect the file
+ descriptors either directly in C or with Python's ``os.dup2`` function
+ in an operating-system dependent way.
+
+.. _eval:
+
Evaluating Python expressions from strings and files
====================================================
-pybind11 provides the :func:`eval` and :func:`eval_file` functions to evaluate
+pybind11 provides the `eval`, `exec` and `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
@@ -48,10 +110,35 @@ is always ``none``).
int result = py::eval("my_variable + 10", scope).cast<int>();
// Evaluate a sequence of statements
- py::eval<py::eval_statements>(
+ py::exec(
"print('Hello')\n"
"print('world!');",
scope);
// Evaluate the statements in an separate Python file on disk
py::eval_file("script.py", scope);
+
+C++11 raw string literals are also supported and quite handy for this purpose.
+The only requirement is that the first statement must be on a new line following
+the raw string delimiter ``R"(``, ensuring all lines have common leading indent:
+
+.. code-block:: cpp
+
+ py::exec(R"(
+ x = get_answer()
+ if x == 42:
+ print('Hello World!')
+ else:
+ print('Bye!')
+ )", scope
+ );
+
+.. note::
+
+ `eval` and `eval_file` accept a template parameter that describes how the
+ string/file 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``). `eval` defaults to ``eval_expr``,
+ `eval_file` defaults to ``eval_statements`` and `exec` is just a shortcut
+ for ``eval<eval_statements>``.