1

how do I pass a python method and kwargs to a boost C++ function and call the python method with kwargs.

python:

def py_method(**kwargs):
    for key in kwargs.keys():
        print 'Key: ', key, ', Value: ', kwargs[key]

cpp_method(py_method, arg1=1, arg2=2)

or

kwargs = {'arg1': 1, 'arg2': 2}
cpp_method(py_method, **kwargs)

C++: please help me to correct the below code.

using namespace boost::python;

void cpp_method(object py_method, object kwargs)
py_method(kwargs)

Thanks to Dan Mašek for pointing this link

Compiled on MacOS HighSierra and getting segmentation fault:

g++ -std=c++11 -I/Library/Frameworks/Python.framework/Versions/2.7/Headers -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"foo.d" -MT"foo.o" -o "foo.o" foo.cpp

g++ -L/usr/local/lib -L/Library/Frameworks/Python.framework/Versions/2.7/ -shared -o foo.so  ./foo.o   -lboost_python27 -lPython

$ python
Python 2.7.14 (v2.7.14:84471935ed, Sep 16 2017, 12:01:12) 
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import foo
>>> dir(foo)
['__doc__', '__file__', '__name__', '__package__', 'cpp_method']
>>> def py_method(**kwargs):
...     print 'from py_method'
...     print kwargs
... 
>>> kwargs = {'arg1': 1, 'arg2': 2}
>>> foo.cpp_method(py_method, kwargs)
Segmentation fault: 11

Process:               Python [22790]
Path:                  /Library/Frameworks/Python.framework/Versions/2.7/Resources/Python.app/Contents/MacOS/Python
Identifier:            Python
Version:               2.7.14 (2.7.14)
Code Type:             X86-64 (Native)
Parent Process:        bash [368]
Responsible:           Python [22790]
User ID:               501

Date/Time:             2018-10-04 16:54:51.618 -0700
OS Version:            Mac OS X 10.13.6 (17G65)
Report Version:        12
Anonymous UUID:        3A7BC812-2E65-69A4-936B-21E5CE648BCF

Sleep/Wake UUID:       E32B82BD-2B4C-4220-A9C2-F71FF57DDA56

Time Awake Since Boot: 580000 seconds
Time Since Wake:       2700 seconds

System Integrity Protection: disabled

Crashed Thread:        0  Dispatch queue: com.apple.main-thread

Exception Type:        EXC_BAD_ACCESS (SIGSEGV)
Exception Codes:       KERN_INVALID_ADDRESS at 0x0000000000000048
Exception Note:        EXC_CORPSE_NOTIFY

Termination Signal:    Segmentation fault: 11
Termination Reason:    Namespace SIGNAL, Code 0xb
Terminating Process:   exc handler [0]

VM Regions Near 0x48:
--> 
    __TEXT                 0000000100000000-0000000100001000 [    4K] r-x/rwx SM=COW  /Library/Frameworks/Python.framework/Versions/2.7/Resources/Python.app/Contents/MacOS/Python

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0   org.python.python               0x00007fff3bfaec5c PyErr_Occurred + 14
1   org.python.python               0x00007fff3bf2bdf5 PyObject_IsInstance + 401
2   foo.so                          0x0000000100799aaf boost::python::converter::pyobject_type::check(_object*) + 31 (pyobject_type.hpp:24)
3   foo.so                          0x0000000100799918 boost::python::converter::object_manager_value_arg_from_python::convertible() const + 24 (obj_mgr_arg_from_python.hpp:69)
4   foo.so                          0x00000001007997e1 boost::python::detail::caller_arity::impl >::operator()(_object*, _object*) + 129 (local.hpp:37)
5   foo.so                          0x00000001007996e4 boost::python::objects::caller_py_function_impl > >::operator()(_object*, _object*) + 52 (py_function.hpp:38)
6   libboost_python27.dylib         0x000000010190e1a4 boost::python::objects::function::call(_object*, _object*) const + 820
7   libboost_python27.dylib         0x0000000101910d5a boost::detail::function::void_function_ref_invoker0::invoke(boost::detail::function::function_buffer&) + 26
8   libboost_python27.dylib         0x0000000101916f48 boost::python::handle_exception_impl(boost::function0) + 72
9   libboost_python27.dylib         0x0000000101910871 boost::python::objects::function_call(_object*, _object*, _object*) + 81
10  org.python.python               0x000000010000c2e2 PyObject_Call + 98
11  org.python.python               0x00000001000c30b1 PyEval_EvalFrameEx + 15777
12  org.python.python               0x00000001000cac23 PyEval_EvalCodeEx + 2115
13  org.python.python               0x00000001000cad46 PyEval_EvalCode + 54
14  org.python.python               0x00000001000ef7ec PyRun_InteractiveOneFlags + 380
15  org.python.python               0x00000001000efa4e PyRun_InteractiveLoopFlags + 78
16  org.python.python               0x00000001000f0261 PyRun_AnyFileExFlags + 161
17  org.python.python               0x00000001001071dd Py_Main + 3101
18  org.python.python               0x0000000100000f14 0x100000000 + 3860

Thread 0 crashed with X86 Thread State (64-bit):
  rax: 0x0000000000000000  rbx: 0x0000000000000002  rcx: 0x0000000000000001  rdx: 0x0000000000000003
  rdi: 0x00007fff8cc80458  rsi: 0x00000001007b4030  rbp: 0x00007ffeefbff210  rsp: 0x00007ffeefbff210
   r8: 0x00000001007b4030   r9: 0x8c8bb1dcac69804a  r10: 0x0000000000001002  r11: 0xffff8001c47c5769
  r12: 0x0000000000000000  r13: 0x0000000100702a70  r14: 0x0000000100728280  r15: 0x00007fff8cc784f0
  rip: 0x00007fff3bfaec5c  rfl: 0x0000000000010246  cr2: 0x0000000000000048

Logical CPU:     3
Error Code:      0x00000004
Trap Number:     14


Binary Images:
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External Modification Summary:
  Calls made by other processes targeting this process:
    task_for_pid: 0
    thread_create: 0
    thread_set_state: 0
  Calls made by this process:
    task_for_pid: 0
    thread_create: 0
    thread_set_state: 0
  Calls made by all processes on this machine:
    task_for_pid: 577992
    thread_create: 0
    thread_set_state: 0

VM Region Summary:
ReadOnly portion of Libraries: Total=213.0M resident=0K(0%) swapped_out_or_unallocated=213.0M(100%)
Writable regions: Total=38.3M written=0K(0%) resident=0K(0%) swapped_out=0K(0%) unallocated=38.3M(100%)

                                VIRTUAL   REGION 
REGION TYPE                        SIZE    COUNT (non-coalesced) 
===========                     =======  ======= 
Activity Tracing                   256K        2 
Kernel Alloc Once                    8K        2 
MALLOC                            29.5M       12 
MALLOC guard page                   16K        5 
STACK GUARD                       56.0M        2 
Stack                             8192K        2 
VM_ALLOCATE                        256K        2 
__DATA                            4532K       57 
__LINKEDIT                       193.6M       10 
__TEXT                            19.4M       55 
__UNICODE                          560K        2 
shared memory                       12K        4 
===========                     =======  ======= 
TOTAL                            312.0M      143 

Model: MacBookPro12,1, BootROM MBP121.0177.B00, 2 processors, Intel Core i7, 3.1 GHz, 16 GB, SMC 2.28f7
Graphics: Intel Iris Graphics 6100, Intel Iris Graphics 6100, Built-In
Memory Module: BANK 0/DIMM0, 8 GB, DDR3, 1867 MHz, 0x02FE, 0x4544464232333241314D412D4A442D460000
Memory Module: BANK 1/DIMM0, 8 GB, DDR3, 1867 MHz, 0x02FE, 0x4544464232333241314D412D4A442D460000
AirPort: spairport_wireless_card_type_airport_extreme (0x14E4, 0x133), Broadcom BCM43xx 1.0 (7.77.37.31.1a9)
Bluetooth: Version 6.0.7f10, 3 services, 27 devices, 1 incoming serial ports
Network Service: Wi-Fi, AirPort, en0
Serial ATA Device: APPLE SSD SM0512G, 500.28 GB
USB Device: USB 3.0 Bus
USB Device: Bluetooth USB Host Controller
Thunderbolt Bus: MacBook Pro, Apple Inc., 27.1
Improve this question
6
  • You want bp::object (holding the python function), and bp::dict holding the kwargs. Then use operator() of the bp::object, which has an overload taking args and kwargs. | Also see here Commented Oct 3, 2018 at 13:39
  • Thank you. the compiler doesn't resolve get_python_func_of_wrapped_object(). doesn't seems like a boost-python function. do you know where does it come from? Commented Oct 3, 2018 at 23:57
  • Oh, in the scope of that example, that's just a placeholder for some c++ function that returns a bp::object representing the python function you want to call. In your case you already have that as py_method argument of cpp_method. Commented Oct 4, 2018 at 0:06
  • 1
    Check this out. This just passes the dictionary containing the arguments directly to the c++ function. Making it with real keyword args, like you show in your code shouldn't be much harder -- i'll check it out later. Commented Oct 4, 2018 at 0:25
  • Thank you so much for the link. that's exactly I was looking for. I am getting a segmentation fault. Not enough space to paste the back trace. Commented Oct 4, 2018 at 5:21

1 Answer 1

Reset to default
0

I solved it with pybind11, much easier than boost-python

cpp.cpp:

#include <pybind11/pybind11.h>
#include <iostream>

namespace py = pybind11;

void cpp_method(py::object method, py::kwargs kw) {
    py::object obj = method(**kw);
    std::cout << "Printing from cpp: " << std::string(py::str(obj)) << std::endl;
}

PYBIND11_MODULE(cpp, mod) {
    mod.def("cpp_method", &cpp_method);
}

compilation:

c++ -O3 -Wall -shared -std=c++11 -fPIC `python -m pybind11 --includes` cpp.cpp -o cpp.so `python-config --ldflags`

python:

$ python
Python 2.7.14 (v2.7.14:84471935ed, Sep 16 2017, 12:01:12) 
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import cpp
>>> dir(cpp)
['__doc__', '__file__', '__name__', '__package__', 'cpp_method']
>>> def py_method(**kwargs):
...     print 'Printing from python, kwargs: ', kwargs
...     return 'py_method return string'
... 
>>> cpp.cpp_method(py_method, a=1, b=2, c=3)
Printing from python, kwargs:  {'a': 1, 'c': 3, 'b': 2}
Printing from cpp: py_method return string
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