2 pybind11/iostream.h -- Tools to assist with redirecting cout and cerr to Python
4 Copyright (c) 2017 Henry F. Schreiner
6 All rights reserved. Use of this source code is governed by a
7 BSD-style license that can be found in the LICENSE file.
20 NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
21 NAMESPACE_BEGIN(detail)
23 // Buffer that writes to Python instead of C++
24 class pythonbuf : public std::streambuf {
26 using traits_type = std::streambuf::traits_type;
28 const size_t buf_size;
29 std::unique_ptr<char[]> d_buffer;
34 if (!traits_type::eq_int_type(c, traits_type::eof())) {
35 *pptr() = traits_type::to_char_type(c);
38 return sync() == 0 ? traits_type::not_eof(c) : traits_type::eof();
42 if (pbase() != pptr()) {
43 // This subtraction cannot be negative, so dropping the sign
44 str line(pbase(), static_cast<size_t>(pptr() - pbase()));
47 gil_scoped_acquire tmp;
52 setp(pbase(), epptr());
59 pythonbuf(object pyostream, size_t buffer_size = 1024)
60 : buf_size(buffer_size),
61 d_buffer(new char[buf_size]),
62 pywrite(pyostream.attr("write")),
63 pyflush(pyostream.attr("flush")) {
64 setp(d_buffer.get(), d_buffer.get() + buf_size - 1);
67 pythonbuf(pythonbuf&&) = default;
69 /// Sync before destroy
79 This a move-only guard that redirects output.
83 #include <pybind11/iostream.h>
88 py::scoped_ostream_redirect output;
89 std::cout << "Hello, World!"; // Python stdout
90 } // <-- return std::cout to normal
92 You can explicitly pass the c++ stream and the python object,
93 for example to guard stderr instead.
98 py::scoped_ostream_redirect output{std::cerr, py::module::import("sys").attr("stderr")};
99 std::cerr << "Hello, World!";
102 class scoped_ostream_redirect {
105 std::ostream &costream;
106 detail::pythonbuf buffer;
109 scoped_ostream_redirect(
110 std::ostream &costream = std::cout,
111 object pyostream = module::import("sys").attr("stdout"))
112 : costream(costream), buffer(pyostream) {
113 old = costream.rdbuf(&buffer);
116 ~scoped_ostream_redirect() {
120 scoped_ostream_redirect(const scoped_ostream_redirect &) = delete;
121 scoped_ostream_redirect(scoped_ostream_redirect &&other) = default;
122 scoped_ostream_redirect &operator=(const scoped_ostream_redirect &) = delete;
123 scoped_ostream_redirect &operator=(scoped_ostream_redirect &&) = delete;
128 Like `scoped_ostream_redirect`, but redirects cerr by default. This class
129 is provided primary to make ``py::call_guard`` easier to make.
133 m.def("noisy_func", &noisy_func,
134 py::call_guard<scoped_ostream_redirect,
135 scoped_estream_redirect>());
138 class scoped_estream_redirect : public scoped_ostream_redirect {
140 scoped_estream_redirect(
141 std::ostream &costream = std::cerr,
142 object pyostream = module::import("sys").attr("stderr"))
143 : scoped_ostream_redirect(costream,pyostream) {}
147 NAMESPACE_BEGIN(detail)
149 // Class to redirect output as a context manager. C++ backend.
150 class OstreamRedirect {
153 std::unique_ptr<scoped_ostream_redirect> redirect_stdout;
154 std::unique_ptr<scoped_estream_redirect> redirect_stderr;
157 OstreamRedirect(bool do_stdout = true, bool do_stderr = true)
158 : do_stdout_(do_stdout), do_stderr_(do_stderr) {}
162 redirect_stdout.reset(new scoped_ostream_redirect());
164 redirect_stderr.reset(new scoped_estream_redirect());
168 redirect_stdout.reset();
169 redirect_stderr.reset();
173 NAMESPACE_END(detail)
176 This is a helper function to add a C++ redirect context manager to Python
177 instead of using a C++ guard. To use it, add the following to your binding code:
181 #include <pybind11/iostream.h>
185 py::add_ostream_redirect(m, "ostream_redirect");
187 You now have a Python context manager that redirects your output:
189 .. code-block:: python
191 with m.ostream_redirect():
192 m.print_to_cout_function()
194 This manager can optionally be told which streams to operate on:
196 .. code-block:: python
198 with m.ostream_redirect(stdout=true, stderr=true):
199 m.noisy_function_with_error_printing()
202 inline class_<detail::OstreamRedirect> add_ostream_redirect(module m, std::string name = "ostream_redirect") {
203 return class_<detail::OstreamRedirect>(m, name.c_str(), module_local())
204 .def(init<bool,bool>(), arg("stdout")=true, arg("stderr")=true)
205 .def("__enter__", &detail::OstreamRedirect::enter)
206 .def("__exit__", [](detail::OstreamRedirect &self_, args) { self_.exit(); });
209 NAMESPACE_END(PYBIND11_NAMESPACE)