I know pickles can be easily loaded into python using
import pickle
p = pickle.load(open("file.pkl"))
I was wondering how to load the same pickle file in pyx/C code in python? I couldn't find the method to directly load it.
Perhaps a solution would be to load in python and pass reference to object in C?
The easy answer would be to just compile your code with Cython. Everything there will be done automatically.
In context of the Python C API, you could easily replicate this code with something like:
PyObject *file = NULL, *p = NULL;
PyObject *pickle = PyImport_ImportModule("pickle"); // import module
if (!pickle) goto error;
file = PyFile_FromString("file.pkl", "r"); // open("file.pkl")
if (!pickle) goto error;
p = PyObject_CallMethod(pickle, "load", "O", file); // pickle.load(file)
error:
Py_XDECREF(pickle);
Py_XDECREF(file);
This is done for Python 2, while for Python 3 open("file.pkl") needs to be implemented by using the io module.
Related
i have a problem with my code.
i have a python file for the capturing of mavlink messages(i'm using pymavlink library) and i need to create a library for interfacing python results with c/c++ code.
this is my python code from .py file
from pymavlink import mavutil
the_connection = mavutil.mavlink_connection('udpin:localhost:14550')
the_connection.wait_heartbeat()
print("Heartbeat from system (system %u component %u)" % (the_connection.target_system, the_connection.target_component))
while 1:
attitude=the_connection.messages['ATTITUDE']
print("attitude: ",attitude)
i need to recover the attitude object as PyObject, the result of the last print is:
attitude: ATTITUDE {time_boot_ms : 1351674, roll : -0.006938610225915909, pitch : -0.009435104206204414, yaw : 1.8100472688674927, rollspeed : 0.0005244240164756775, pitchspeed : -0.0023000920191407204, yawspeed : 0.0002169199287891388}
i have a streaming of messages, so i need to call the connection and the to evaluate the result in a loop. so i tried to call the simple python commands as string, to open the connection and then access to the data. My C code is:
Py_Initialize();
PyRun_SimpleString("from pymavlink import mavutil\n"
"the_connection = mavutil.mavlink_connection('udpin:localhost:14550')\n"
"the_connection.wait_heartbeat()\n"
"print(\"Heartbeat from system (system %u component %u)\" % (the_connection.target_system, the_connection.target_component), flush=True)" );
PyObject* main_module=PyImport_AddModule("__main__");
PyObject* pdict = PyModule_GetDict(main_module);
PyObject* pdict_new = PyDict_New();
while (1) {
PyObject* pval = PyRun_String("the_connection.messages['ATTITUDE']", Py_single_input, pdict, pdict_new);
PyObject* repr = PyObject_Str(pval);
PyObject* str = PyUnicode_AsEncodedString(repr, "utf-8", "~E~");
const char* bytes = PyBytes_AS_STRING(str);
PyObject_Print(pval, stdout, 0);
printf(" end\n");
Py_XDECREF(repr);
}
Py_Finalize();
the result of this code is:
<pymavlink.dialects.v20.ardupilotmega.MAVLink_attitude_message object at 0x7fba218220>
None end
<pymavlink.dialects.v20.ardupilotmega.MAVLink_attitude_message object at 0x7fba218220>
None end
<pymavlink.dialects.v20.ardupilotmega.MAVLink_attitude_message object at 0x7fba218220>
None end
<pymavlink.dialects.v20.ardupilotmega.MAVLink_attitude_message object at 0x7fba218220>
None end
i've tried using a return of the object, but it didn't work
PyObject* pval = PyRun_String("return(the_connection.messages['ATTITUDE'])", Py_single_input, pdict, pdict_new);
i'm not expert of C/C++, is there a way to obtain the result in the right way?i'm not interested in a string format, i only need a way to use the result as c object
i'm using python 3.9, on a raspberry pi, gcc version is 10.2.1.
thank you
You want
PyRun_String("the_connection.messages['ATTITUDE']", Py_eval_input, pdict, pdict_new);
Py_eval_input treats it like the Python builtin eval (so what you're running must be an expression rather than a statement, which it is...).
In contrast, Py_single_input evaluates a single statement, but just returns None because a statement doesn't necessary returns anything. (In Python all expressions are statements, but not all statements are expressions). It's more akin to exec (but only deals with a single line).
Using "return(the_connection.messages['ATTITUDE'])" doesn't work because return is specifically designed to appear in a Python function.
I am totally new to boost.python.
I reviewed a lot of recommending of using boost.python to apply with python, however still not easy to understand and find a solution for me.
What I want is to import a function or class that directly from a python "SourceFile"
Example File:
Main.cpp
MyPythonClass.py
Let's says if there is a "Dog" class in "MyPythonClass.py" with "bark()" function, how do I get callback and send argument in cpp?
I have no idea what I should do!
Please help me!
When one needs to call Python from C++, and C++ owns the main function, then one must embed the Python interrupter within the C++ program. The Boost.Python API is not a complete wrapper around the Python/C API, so one may find the need to directly invoke parts of the Python/C API. Nevertheless, Boost.Python's API can make interoperability easier. Consider reading the official Boost.Python embedding tutorial for more information.
Here is a basic skeleton for a C++ program that embeds Python:
int main()
{
// Initialize Python.
Py_Initialize();
namespace python = boost::python;
try
{
... Boost.Python calls ...
}
catch (const python::error_already_set&)
{
PyErr_Print();
return 1;
}
// Do not call Py_Finalize() with Boost.Python.
}
When embedding Python, it may be necessary to augment the module search path via PYTHONPATH so that modules can be imported from custom locations.
// Allow Python to load modules from the current directory.
setenv("PYTHONPATH", ".", 1);
// Initialize Python.
Py_Initialize();
Often times, the Boost.Python API provides a way to write C++ code in a Python-ish manner. The following example demonstrates embedding a Python interpreter in C++, and having C++ import a MyPythonClass Python module from disk, instantiate an instance of MyPythonClass.Dog, and then invoking bark() on the Dog instance:
#include <boost/python.hpp>
#include <cstdlib> // setenv
int main()
{
// Allow Python to load modules from the current directory.
setenv("PYTHONPATH", ".", 1);
// Initialize Python.
Py_Initialize();
namespace python = boost::python;
try
{
// >>> import MyPythonClass
python::object my_python_class_module = python::import("MyPythonClass");
// >>> dog = MyPythonClass.Dog()
python::object dog = my_python_class_module.attr("Dog")();
// >>> dog.bark("woof");
dog.attr("bark")("woof");
}
catch (const python::error_already_set&)
{
PyErr_Print();
return 1;
}
// Do not call Py_Finalize() with Boost.Python.
}
Given a MyPythonClass module that contains:
class Dog():
def bark(self, message):
print "The dog barks: {}".format(message)
The above program outputs:
The dog barks: woof
Boost python is used to call cplusplus functions from a python source. Pretty much like the Perl xs module.
If you have a function say bark() in main.cpp, you can use boost python to convert this main.cpp into a python callable module.
Then from python script(assuming link output file is main.so):
import main
main.bark()
I'm trying to embed Python in my C++ application, somewhat akin to the method found here in section 1.4:
https://docs.python.org/3.5/extending/embedding.html
The synopsis of the problem I'm having is that I can't get the C++ application to work with .py files that import the 'emb' module, ie, the Python extension module that's written into the C++ code.
I have a Python file, testmod.py:
import emb
# define some functions
def printhello(input):
emb.numargs()
return 2
def timesfour(input):
print(input * 4)
In my C++ application, I have this code which works:
PyImport_AppendInittab("emb", &(mynamespace::PyInit_emb) );
Py_Initialize();
PyObject *globals = PyModule_GetDict(PyImport_AddModule("__main__"));
PyObject *testModule = PyImport_ImportModule("emb");
PyObject* pFunc = PyObject_GetAttrString(testModule, "numargs");
After this, pFunc is non-NULL; things look good. So I think the 'embedded module' is fine.
If I change the last two lines from above to:
PyObject* testModule = PyImport_ImportModule("testmod");
PyObject* pFunc = PyObject_GetAttrString(testModule, "printhello");
This also works fine, provided the line emb.numargs() is removed from testmod.py Once I add that line, and re-run the C++ application, testModule becomes NULL, which means something has gone wrong.
Any ideas?
Is this the way this capability is supposed to be used?
I would like to call PARI/GP from Python only to calculate the function nextprime(n) for different ns that I define. Unfortunately I can't get pari-python to install so I thought I would just call it using a command line via os.system in Python. I can't see in the man page how to do get PARI/GP to run in non-interactive mode, however. Is there a way to achieve this?
You can pipe input into gp's stdin like so, using the -q flag to quash verbosity:
senderle:~ $ echo "print(isprime(5))" | gp -q
1
However, it's not much harder to create a simple python extension that allows you to pass strings to pari's internal parser and get results back (as strings). Here's a bare-bones version that I wrote some time ago so that I could call pari's implementation of the APRT test from python. You could extend this further to do appropriate conversions and so on.
//pariparse.c
#include<Python.h>
#include<pari/pari.h>
static PyObject * pariparse_run(PyObject *self, PyObject *args) {
pari_init(40000000, 2);
const char *pari_code;
char *outstr;
if (!PyArg_ParseTuple(args, "s", &pari_code)) { return NULL; }
outstr = GENtostr(gp_read_str(pari_code));
pari_close();
return Py_BuildValue("s", outstr);
}
static PyMethodDef PariparseMethods[] = {
{"run", pariparse_run, METH_VARARGS, "Run a pari command."},
{NULL, NULL, 0, NULL}
};
PyMODINIT_FUNC initpariparse(void) {
(void) Py_InitModule("pariparse", PariparseMethods);
}
And the setup file:
#setup.py
from distutils.core import setup, Extension
module1 = Extension('pariparse',
include_dirs = ['/usr/include', '/usr/local/include'],
libraries = ['pari'],
library_dirs = ['/usr/lib', '/usr/local/lib'],
sources = ['pariparse.c'])
setup (name = 'pariparse',
version = '0.01a',
description = 'A super tiny python-pari interface',
ext_modules = [module1])
Then just type python setup.py build to build the extension. You can then call it like this:
>>> pariparse.run('nextprime(5280)')
'5281'
I tested this just now and it compiled for me with the latest version of pari available via homebrew (on OS X). YMMV!
You might want to try using the Sage math tool. Sage uses Python to glue together all sorts of math libraries, including PARI. Some of the math libraries are nicely integrated, others use hacks (passing strings in to the library and then parsing out the string results) but in all cases someone else did the integration work for you and you can just use it.
You can set up your own Sage system, or you can get a free account and try Sage on the University of Washington servers.
I don't think it is a good idea to call os.system except for a quick and dirty workaround when you have a reliable C library behind it. It is very easy to call C functions from Python; here are two functions for calling nextprime. One is using long integers (despite the name, it will mean here that you are using small integer numbers); the other is using the string type (for longer integers).
First check that you have the libpari installed. The solution below is for Linux and assumes that your library is called libpari.so. Under Windows it will probably be called with a .dll suffix instead. You may have to type the whole path of the DLL file if it isn't found at first attempt:
import ctypes
# load the library
pari=ctypes.cdll.LoadLibrary("libpari.so")
# set the right return type of the functions
pari.stoi.restype = ctypes.POINTER(ctypes.c_long)
pari.nextprime.restype = ctypes.POINTER(ctypes.c_long)
pari.strtoGENstr.restype = ctypes.POINTER(ctypes.c_long)
pari.geval.restype = ctypes.POINTER(ctypes.c_long)
pari.itostr.restype = ctypes.c_char_p
# initialize the library
pari.pari_init(2**19,0)
def nextprime(v):
g = pari.nextprime(pari.stoi(ctypes.c_long(v)))
return pari.itos(g)
def nextprime2(v):
g = pari.nextprime(pari.geval(pari.strtoGENstr(str(v))))
return int(pari.itostr(g))
print( nextprime(456) )
print( nextprime2(456) )
I'm trying to call some function from Kernel32.dll in my Python script running on Linux. As Johannes Weiß pointed How to call Wine dll from python on Linux? I'm loading kernel32.dll.so library via ctypes.cdll.LoadLibrary() and it loads fine. I can see kernel32 loaded and even has GetLastError() function inside. However whenever I'm trying to call the function i'm gettings segfault.
import ctypes
kernel32 = ctypes.cdll.LoadLibrary('/usr/lib/i386-linux-gnu/wine/kernel32.dll.so')
print kernel32
# <CDLL '/usr/lib/i386-linux-gnu/wine/kernel32.dll.so', handle 8843c10 at b7412e8c>
print kernel32.GetLastError
# <_FuncPtr object at 0xb740b094>
gle = kernel32.GetLastError
# OK
gle_result = gle()
# fails with
# Segmentation fault (core dumped)
print gle_result
First I was thinking about calling convention differences but it seems to be okay after all. I'm ending with testing simple function GetLastError function without any params but I'm still getting Segmentation fault anyway.
My testing system is Ubuntu 12.10, Python 2.7.3 and wine-1.4.1 (everything is 32bit)
UPD
I proceed with my testing and find several functions that I can call via ctypes without segfault. For instance I can name Beep() and GetCurrentThread() functions, many other functions still give me segfault. I created a small C application to test kernel32.dll.so library without python but i've got essentially the same results.
int main(int argc, char **argv)
{
void *lib_handle;
#define LOAD_LIBRARY_AS_DATAFILE 0x00000002
long (*GetCurrentThread)(void);
long (*beep)(long,long);
void (*sleep)(long);
long (*LoadLibraryExA)(char*, long, long);
long x;
char *error;
lib_handle = dlopen("/usr/local/lib/wine/kernel32.dll.so", RTLD_LAZY);
if (!lib_handle)
{
fprintf(stderr, "%s\n", dlerror());
exit(1);
}
// All the functions are loaded e.g. sleep != NULL
GetCurrentThread = dlsym(lib_handle, "GetCurrentThread");
beep = dlsym(lib_handle, "Beep");
LoadLibraryExA = dlsym(lib_handle, "LoadLibraryExA");
sleep = dlsym(lib_handle, "Sleep");
if ((error = dlerror()) != NULL)
{
fprintf(stderr, "%s\n", error);
exit(1);
}
// Works
x = (*GetCurrentThread)();
printf("Val x=%d\n",x);
// Works (no beeping, but no segfault too)
(*beep)(500,500);
// Segfault
(*sleep)(5000);
// Segfault
(*LoadLibraryExA)("/home/ubuntu/test.dll",0,LOAD_LIBRARY_AS_DATAFILE);
printf("The End\n");
dlclose(lib_handle);
return 0;
}
I was trying to use different calling conventions for Sleep() function but got no luck with it too. When I comparing function declarations\implementation in Wine sources they are essentially the same
Declarations
HANDLE WINAPI GetCurrentThread(void) // http://source.winehq.org/source/dlls/kernel32/thread.c#L573
BOOL WINAPI Beep( DWORD dwFreq, DWORD dwDur ) // http://source.winehq.org/source/dlls/kernel32/console.c#L354
HMODULE WINAPI DECLSPEC_HOTPATCH LoadLibraryExA(LPCSTR libname, HANDLE hfile, DWORD flags) // http://source.winehq.org/source/dlls/kernel32/module.c#L928
VOID WINAPI DECLSPEC_HOTPATCH Sleep( DWORD timeout ) // http://source.winehq.org/source/dlls/kernel32/sync.c#L95
WINAPI is defined to be __stdcall
However some of them works and some don't. As I can understand this sources are for kernel32.dll file and kernel32.dll.so file is a some kind of proxy that supposed to provide access to kernel32.dll for linux code. Probably I need to find exact sources of kernel32.dll.so file and take a look on declarations.
Is there any tool I can use to take a look inside .so file and find out what functions and what calling conventions are used?
The simplest way to examine a DLL is to use the nm command, i.e.
$ nm kernel32.dll.so | grep GetLastError
7b86aae0 T _GetLastError
As others have pointed out, the default calling convention for Windows C DLLs is stdcall. It has nothing to do with using Python. On the Windows platform, ctypes.windll is available.
However, I am not even sure what you are trying to do is at all possible. Wine is a full-blown Windows emulator and it is safe to guess that at least you would have to start it with wine_init before loading any other functions. The Windows API probably have some state (set when Windows boots).
The easiest way to continue is probably to install a Windows version of Python under Wine and run your script from there.