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gh-92135: Fix _Py_reinterpret_cast() for const (#92138)
Fix C++ compiler warnings on cast macros, like _PyObject_CAST(), when casting a constant expression to a non constant type: use const_cast<> in C++. * In C++, Py_SAFE_DOWNCAST() now uses static_cast<> rather than reinterpret_cast<>. * Add tests to the _testcppext C++ extension. * test_cppext no longer captures stdout in verbose mode.
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5 changed files with 62 additions and 14 deletions
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@ -43,8 +43,7 @@ typedef PyObject *(*PyCMethod)(PyObject *, PyTypeObject *, PyObject *const *,
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// it triggers an undefined behavior when Python calls it with 2 parameters
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// it triggers an undefined behavior when Python calls it with 2 parameters
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// (bpo-33012).
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// (bpo-33012).
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#define _PyCFunction_CAST(func) \
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#define _PyCFunction_CAST(func) \
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_Py_reinterpret_cast(PyCFunction, \
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_Py_reinterpret_cast(PyCFunction, _Py_reinterpret_cast(void(*)(void), (func)))
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_Py_reinterpret_cast(void(*)(void), (func)))
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PyAPI_FUNC(PyCFunction) PyCFunction_GetFunction(PyObject *);
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PyAPI_FUNC(PyCFunction) PyCFunction_GetFunction(PyObject *);
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PyAPI_FUNC(PyObject *) PyCFunction_GetSelf(PyObject *);
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PyAPI_FUNC(PyObject *) PyCFunction_GetSelf(PyObject *);
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@ -182,9 +182,9 @@ PyAPI_FUNC(void) PyObject_GC_UnTrack(void *);
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PyAPI_FUNC(void) PyObject_GC_Del(void *);
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PyAPI_FUNC(void) PyObject_GC_Del(void *);
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#define PyObject_GC_New(type, typeobj) \
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#define PyObject_GC_New(type, typeobj) \
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_Py_reinterpret_cast(type*, _PyObject_GC_New(typeobj))
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_Py_reinterpret_cast(type*, _PyObject_GC_New(typeobj))
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#define PyObject_GC_NewVar(type, typeobj, n) \
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#define PyObject_GC_NewVar(type, typeobj, n) \
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_Py_reinterpret_cast(type*, _PyObject_GC_NewVar((typeobj), (n)))
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_Py_reinterpret_cast(type*, _PyObject_GC_NewVar((typeobj), (n)))
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PyAPI_FUNC(int) PyObject_GC_IsTracked(PyObject *);
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PyAPI_FUNC(int) PyObject_GC_IsTracked(PyObject *);
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PyAPI_FUNC(int) PyObject_GC_IsFinalized(PyObject *);
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PyAPI_FUNC(int) PyObject_GC_IsFinalized(PyObject *);
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@ -14,10 +14,20 @@
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#endif
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#endif
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// Macro to use C++ static_cast<> and reinterpret_cast<> in the Python C API
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// Macro to use C++ static_cast<>, reinterpret_cast<> and const_cast<>
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// in the Python C API.
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//
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// In C++, _Py_reinterpret_cast(type, expr) converts a constant expression to a
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// non constant type using const_cast<type>. For example,
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// _Py_reinterpret_cast(PyObject*, op) can convert a "const PyObject*" to
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// "PyObject*".
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//
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// The type argument must not be constant. For example, in C++,
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// _Py_reinterpret_cast(const PyObject*, expr) fails with a compiler error.
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#ifdef __cplusplus
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#ifdef __cplusplus
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# define _Py_static_cast(type, expr) static_cast<type>(expr)
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# define _Py_static_cast(type, expr) static_cast<type>(expr)
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# define _Py_reinterpret_cast(type, expr) reinterpret_cast<type>(expr)
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# define _Py_reinterpret_cast(type, expr) \
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const_cast<type>(reinterpret_cast<const type>(expr))
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#else
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#else
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# define _Py_static_cast(type, expr) ((type)(expr))
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# define _Py_static_cast(type, expr) ((type)(expr))
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# define _Py_reinterpret_cast(type, expr) ((type)(expr))
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# define _Py_reinterpret_cast(type, expr) ((type)(expr))
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@ -307,10 +317,10 @@ extern "C" {
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*/
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*/
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#ifdef Py_DEBUG
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#ifdef Py_DEBUG
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# define Py_SAFE_DOWNCAST(VALUE, WIDE, NARROW) \
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# define Py_SAFE_DOWNCAST(VALUE, WIDE, NARROW) \
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(assert((WIDE)(NARROW)(VALUE) == (VALUE)), (NARROW)(VALUE))
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(assert(_Py_static_cast(WIDE, _Py_static_cast(NARROW, (VALUE))) == (VALUE)), \
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_Py_static_cast(NARROW, (VALUE)))
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#else
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#else
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# define Py_SAFE_DOWNCAST(VALUE, WIDE, NARROW) \
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# define Py_SAFE_DOWNCAST(VALUE, WIDE, NARROW) _Py_static_cast(NARROW, (VALUE))
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_Py_reinterpret_cast(NARROW, (VALUE))
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#endif
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#endif
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@ -1,6 +1,9 @@
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// gh-91321: Very basic C++ test extension to check that the Python C API is
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// gh-91321: Very basic C++ test extension to check that the Python C API is
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// compatible with C++ and does not emit C++ compiler warnings.
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// compatible with C++ and does not emit C++ compiler warnings.
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// Always enable assertions
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#undef NDEBUG
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#include "Python.h"
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#include "Python.h"
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PyDoc_STRVAR(_testcppext_add_doc,
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PyDoc_STRVAR(_testcppext_add_doc,
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@ -20,8 +23,36 @@ _testcppext_add(PyObject *Py_UNUSED(module), PyObject *args)
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}
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}
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static PyObject *
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test_api_casts(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
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{
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PyObject *obj = Py_BuildValue("(ii)", 1, 2);
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if (obj == nullptr) {
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return nullptr;
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}
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// gh-92138: For backward compatibility, functions of Python C API accepts
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// "const PyObject*". Check that using it does not emit C++ compiler
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// warnings.
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const PyObject *const_obj = obj;
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Py_INCREF(const_obj);
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Py_DECREF(const_obj);
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PyTypeObject *type = Py_TYPE(const_obj);
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assert(Py_REFCNT(const_obj) >= 1);
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assert(type == &PyTuple_Type);
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assert(PyTuple_GET_SIZE(const_obj) == 2);
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PyObject *one = PyTuple_GET_ITEM(const_obj, 0);
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assert(PyLong_AsLong(one) == 1);
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Py_DECREF(obj);
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Py_RETURN_NONE;
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}
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static PyMethodDef _testcppext_methods[] = {
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static PyMethodDef _testcppext_methods[] = {
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{"add", _testcppext_add, METH_VARARGS, _testcppext_add_doc},
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{"add", _testcppext_add, METH_VARARGS, _testcppext_add_doc},
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{"test_api_casts", test_api_casts, METH_NOARGS, NULL},
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{nullptr, nullptr, 0, nullptr} /* sentinel */
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{nullptr, nullptr, 0, nullptr} /* sentinel */
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};
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};
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@ -1,5 +1,6 @@
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# gh-91321: Build a basic C++ test extension to check that the Python C API is
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# gh-91321: Build a basic C++ test extension to check that the Python C API is
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# compatible with C++ and does not emit C++ compiler warnings.
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# compatible with C++ and does not emit C++ compiler warnings.
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import contextlib
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import os
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import os
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import sys
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import sys
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import unittest
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import unittest
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@ -39,17 +40,24 @@ class TestCPPExt(unittest.TestCase):
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sources=[SOURCE],
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sources=[SOURCE],
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language='c++',
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language='c++',
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extra_compile_args=CPPFLAGS)
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extra_compile_args=CPPFLAGS)
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capture_stdout = (not support.verbose)
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try:
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try:
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try:
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try:
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with (support.captured_stdout() as stdout,
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if capture_stdout:
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support.swap_attr(sys, 'argv', ['setup.py', 'build_ext'])):
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stdout = support.captured_stdout()
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else:
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print()
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stdout = contextlib.nullcontext()
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with (stdout,
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support.swap_attr(sys, 'argv', ['setup.py', 'build_ext', '--verbose'])):
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setup(name="_testcppext", ext_modules=[cpp_ext])
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setup(name="_testcppext", ext_modules=[cpp_ext])
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return
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return
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except:
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except:
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# Show output on error
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if capture_stdout:
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print()
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# Show output on error
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print(stdout.getvalue())
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print()
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print(stdout.getvalue())
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raise
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raise
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except SystemExit:
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except SystemExit:
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self.fail("Build failed")
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self.fail("Build failed")
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