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/*
pybind11/iostream.h -- Tools to assist with redirecting cout and cerr to Python
Copyright (c) 2017 Henry F. Schreiner
All rights reserved. Use of this source code is governed by a
BSD-style license that can be found in the LICENSE file.
*/
#pragma once
#include "pybind11.h"
#include <streambuf>
#include <ostream>
#include <string>
#include <memory>
#include <iostream>
NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
NAMESPACE_BEGIN(detail)
// Buffer that writes to Python instead of C++
class pythonbuf : public std::streambuf {
private:
using traits_type = std::streambuf::traits_type;
char d_buffer[1024];
object pywrite;
object pyflush;
int overflow(int c) {
if (!traits_type::eq_int_type(c, traits_type::eof())) {
*pptr() = traits_type::to_char_type(c);
pbump(1);
}
return sync() ? traits_type::not_eof(c) : traits_type::eof();
}
int sync() {
if (pbase() != pptr()) {
// This subtraction cannot be negative, so dropping the sign
str line(pbase(), static_cast<size_t>(pptr() - pbase()));
pywrite(line);
pyflush();
setp(pbase(), epptr());
}
return 0;
}
public:
pythonbuf(object pyostream)
: pywrite(pyostream.attr("write")),
pyflush(pyostream.attr("flush")) {
setp(d_buffer, d_buffer + sizeof(d_buffer) - 1);
}
/// Sync before destroy
~pythonbuf() {
sync();
}
};
NAMESPACE_END(detail)
/** \rst
This a move-only guard that redirects output.
.. code-block:: cpp
#include <pybind11/iostream.h>
...
{
py::scoped_ostream_redirect output;
std::cout << "Hello, World!"; // Python stdout
} // <-- return std::cout to normal
You can explicitly pass the c++ stream and the python object,
for example to guard stderr instead.
.. code-block:: cpp
{
py::scoped_ostream_redirect output{std::cerr, py::module::import("sys").attr("stderr")};
std::cerr << "Hello, World!";
}
\endrst */
class scoped_ostream_redirect {
protected:
std::streambuf *old;
std::ostream &costream;
detail::pythonbuf buffer;
public:
scoped_ostream_redirect(
std::ostream &costream = std::cout,
object pyostream = module::import("sys").attr("stdout"))
: costream(costream), buffer(pyostream) {
old = costream.rdbuf(&buffer);
}
~scoped_ostream_redirect() {
costream.rdbuf(old);
}
scoped_ostream_redirect(const scoped_ostream_redirect &) = delete;
scoped_ostream_redirect(scoped_ostream_redirect &&other) = default;
scoped_ostream_redirect &operator=(const scoped_ostream_redirect &) = delete;
scoped_ostream_redirect &operator=(scoped_ostream_redirect &&) = delete;
};
/** \rst
Like `scoped_ostream_redirect`, but redirects cerr by default. This class
is provided primary to make ``py::call_guard`` easier to make.
.. code-block:: cpp
m.def("noisy_func", &noisy_func,
py::call_guard<scoped_ostream_redirect,
scoped_estream_redirect>());
\endrst */
class scoped_estream_redirect : public scoped_ostream_redirect {
public:
scoped_estream_redirect(
std::ostream &costream = std::cerr,
object pyostream = module::import("sys").attr("stderr"))
: scoped_ostream_redirect(costream,pyostream) {}
};
NAMESPACE_BEGIN(detail)
// Class to redirect output as a context manager. C++ backend.
class OstreamRedirect {
bool do_stdout_;
bool do_stderr_;
std::unique_ptr<scoped_ostream_redirect> redirect_stdout;
std::unique_ptr<scoped_estream_redirect> redirect_stderr;
public:
OstreamRedirect(bool do_stdout = true, bool do_stderr = true)
: do_stdout_(do_stdout), do_stderr_(do_stderr) {}
void enter() {
if (do_stdout_)
redirect_stdout.reset(new scoped_ostream_redirect());
if (do_stderr_)
redirect_stderr.reset(new scoped_estream_redirect());
}
void exit() {
redirect_stdout.reset();
redirect_stderr.reset();
}
};
NAMESPACE_END(detail)
/** \rst
This is a helper function to add a C++ redirect context manager to Python
instead of using a C++ guard. To use it, add the following to your binding code:
.. code-block:: cpp
#include <pybind11/iostream.h>
...
py::add_ostream_redirect(m, "ostream_redirect");
You now have a Python context manager that redirects your output:
.. code-block:: python
with m.ostream_redirect():
m.print_to_cout_function()
This manager can optionally be told which streams to operate on:
.. code-block:: python
with m.ostream_redirect(stdout=true, stderr=true):
m.noisy_function_with_error_printing()
\endrst */
inline class_<detail::OstreamRedirect> add_ostream_redirect(module m, std::string name = "ostream_redirect") {
return class_<detail::OstreamRedirect>(m, name.c_str(), module_local())
.def(init<bool,bool>(), arg("stdout")=true, arg("stderr")=true)
.def("__enter__", &detail::OstreamRedirect::enter)
.def("__exit__", [](detail::OstreamRedirect &self, args) { self.exit(); });
}
NAMESPACE_END(PYBIND11_NAMESPACE)
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