如何在c ++代码中捕捉python stdout [英] How To catch python stdout in c++ code
问题描述
我有一个程序，在它运行时有时需要调用python以完成一些任务。我需要一个函数调用python和 catches pythons stdout 并把它放在一些文件。
这是函数的声明
pythonCallBackFunc（const char * pythonInput）
我的问题是捕获给定命令的所有python输出（pythonInput）。
我没有python API的经验，我不知道什么是正确的技术来做到这一点。
我试过的第一件事是使用Py_run_SimpleString重定向python的sdtout和stderr
这是我写的代码的一个例子。
#includeboost\python.hpp
#include< iostream>
void pythonCallBackFunc（const char * inputStr）{
PyRun_SimpleString（inputStr）;
}
int main（）{
...
// S0me外部函数这样做
Py_Initialize（）;
PyRun_SimpleString（import sys）;
PyRun_SimpleString（old_stdout = sys.stdout）;
PyRun_SimpleString（fsock = open（'python_out.log'，'a'））;
PyRun_SimpleString（sys.stdout = fsock）;
...
// my func
pythonCallBackFunc（print'HAHAHAHAHA'）;
pythonCallBackFunc（result = 5）;
pythonCallBackFunc（print result）;
pythonCallBackFunc（result ='Hello'+'World！'）;
pythonCallBackFunc（print result）;
pythonCallBackFunc（'KUKU'+'KAKA'）;
pythonCallBackFunc（5 ** 3）;
pythonCallBackFunc（prinhghult）;
pythonCallBackFunc（execfile（'stdout_close.py'））;
...
//另一个函数代码
PyRun_SimpleString（sys.stdout = old_stdout）;
PyRun_SimpleString（fsock.close（））;
Py_Finalize（）;
return 0;
}
有更好的方法吗？此外，由于某些原因，当PyRun_SimpleString获取一些数学表达式时，PyRun_SimpleString不会执行任何操作，例如PyRun_SimpleString（5 ** 3）什么也不打印（python conlsul打印结果：125）
也许这很重要，我使用visual studio 2008.
谢谢，
Alex
根据Mark的建议做出的更改：
#include< python.h>
#include< string>
using namespace std;
void PythonPrinting（string inputStr）{
string stdOutErr =
import sys\\\
\
class CatchOut：\\\
\
def __init __（self）：\\\
\
self.value =''\\\
\
def write（self，txt）：\\\
\
self.value + = txt\\\
\
catchOut = CatchOut（）\\\
\
sys.stdout = catchOut\\\
\
sys.stderr = catchOut\\\
\
; //这是python代码重定向stdouts / stderr
PyObject * pModule = PyImport_AddModule（__ main__）; // create main module
PyRun_SimpleString（stdOutErr.c_str（））; //调用代码重定向
PyRun_SimpleString（inputStr.c_str（））;
PyObject * catcher = PyObject_GetAttrString（pModule，catchOut）;
PyObject * output = PyObject_GetAttrString（catcher，value）;
printf（这里是输出：％s\\\
，PyString_AsString（output））;
}
int main（int argc，char ** argv）{
Py_Initialize（）;
PythonPrinting（print 123）;
PythonPrinting（1 + 5）;
PythonPrinting（result = 2）;
PythonPrinting（print result）;
Py_Finalize（）;
return 0;
}
运行main后得到的输出：
这里是输出：123
下面是输出：
下面是输出：
这里是输出：2
这对我很好，但只有一个问题，应该是
这里是输出：123
这里是输出：6
这里是输出：
这里是输出：2
我不知道为什么，但运行此命令后：PythonPrinting 5），PyString_AsString（output）命令返回一个空字符串（char *）而不是6 ... :(有一些我不能松开这个输出？
Thaks，
Alex
如果我正确地读取你的问题，你想捕获stdout / stderr你可以通过重定向stdout / stderr到一个python变量，然后查询这个变量到你的C ++。请不要，我没有做适当的计数如下：
#include< Python.h>
#include< string>
int main（int argc，char ** argv）
{
std :: string stdOutErr =
import sys\\\
\
class CatchOutErr：\\\
\
def __init __（self）：\\\
\
self.value =''\\\
\
def write（self，txt）： \\\
\
self.value + = txt\\\
\
catchOutErr = CatchOutErr（）\\\
\
sys.stdout = catchOutErr\\\
\
sys.stderr = catchOutErr\\\
\
; //这是python代码重定向stdouts / stderr
Py_Initialize（）;
PyObject * pModule = PyImport_AddModule（__ main__）; // create main module
PyRun_SimpleString（stdOutErr.c_str（））; //调用代码重定向
PyRun_SimpleString（print（1 + 1））; // this is ok stdout
PyRun_SimpleString（1 + a）; // this creating a error
PyObject * catcher = PyObject_GetAttrString（pModule，catchOutErr）; // get our catchOutErr created above
PyErr_Print（）; // make python print any errors
PyObject * output = PyObject_GetAttrString（catcher，value）; //从我们的catchOutErr对象获取stdout和stderr
printf（这里是输出：\\\
％s，PyString_AsString（output））; //它不在我们的C ++部分
Py_Finalize（）;
return 0;
}
I have a program which during it's run sometimes needs to call python in order to preform some tasks. I need a function that calls python and catches pythons stdout and puts it in some file. This is a declaration of the function
pythonCallBackFunc(const char* pythonInput)
My problem is to catch all the python output for a given command (pythonInput). I have no experience with python API and I don't know what is the right technique to do this. First thing I've tried is to redirect python's sdtout and stderr using Py_run_SimpleString this is some example of the code i've written.
#include "boost\python.hpp"
#include <iostream>
void pythonCallBackFunc(const char* inputStr){
PyRun_SimpleString(inputStr);
}
int main () {
...
//S0me outside functions does this
Py_Initialize();
PyRun_SimpleString("import sys");
PyRun_SimpleString("old_stdout = sys.stdout");
PyRun_SimpleString("fsock = open('python_out.log','a')");
PyRun_SimpleString("sys.stdout = fsock");
...
//my func
pythonCallBackFunc("print 'HAHAHAHAHA'");
pythonCallBackFunc("result = 5");
pythonCallBackFunc("print result");
pythonCallBackFunc("result = 'Hello '+'World!'");
pythonCallBackFunc("print result");
pythonCallBackFunc("'KUKU '+'KAKA'");
pythonCallBackFunc("5**3");
pythonCallBackFunc("prinhghult");
pythonCallBackFunc("execfile('stdout_close.py')");
...
//Again anothers function code
PyRun_SimpleString("sys.stdout = old_stdout");
PyRun_SimpleString("fsock.close()");
Py_Finalize();
return 0;
}
Is there a better way to do this? Besides, for some reason PyRun_SimpleString does nothing when it gets some mathematical expression, for example PyRun_SimpleString("5**3") prints nothing (python conlsul prints the result: 125)
maybe it is important, i am using visual studio 2008. Thanks, Alex
Changes I've made according Mark's suggestion:
#include <python.h>
#include <string>
using namespace std;
void PythonPrinting(string inputStr){
string stdOutErr =
"import sys\n\
class CatchOut:\n\
def __init__(self):\n\
self.value = ''\n\
def write(self, txt):\n\
self.value += txt\n\
catchOut = CatchOut()\n\
sys.stdout = catchOut\n\
sys.stderr = catchOut\n\
"; //this is python code to redirect stdouts/stderr
PyObject *pModule = PyImport_AddModule("__main__"); //create main module
PyRun_SimpleString(stdOutErr.c_str()); //invoke code to redirect
PyRun_SimpleString(inputStr.c_str());
PyObject *catcher = PyObject_GetAttrString(pModule,"catchOut");
PyObject *output = PyObject_GetAttrString(catcher,"value");
printf("Here's the output: %s\n", PyString_AsString(output));
}
int main(int argc, char** argv){
Py_Initialize();
PythonPrinting("print 123");
PythonPrinting("1+5");
PythonPrinting("result = 2");
PythonPrinting("print result");
Py_Finalize();
return 0;
}
The output i get after running main:
Here's the output: 123
Here's the output:
Here's the output:
Here's the output: 2
It is good for me , but only one problem, it should be
Here's the output: 123
Here's the output: 6
Here's the output:
Here's the output: 2
I dont know why but after running this command: PythonPrinting("1+5"), PyString_AsString(output) command returns an empty string (char*) instead of 6... :( Is there somthing i can do not to loose this output?
Thaks, Alex
If I'm reading your question correctly, you want to capture stdout/stderr into a variable within your C++? You can do this by redirecting stdout/stderr into a python variable and then querying this variable into your C++. Please not that I have not done the proper ref counting below:
#include <Python.h>
#include <string>
int main(int argc, char** argv)
{
std::string stdOutErr =
"import sys\n\
class CatchOutErr:\n\
def __init__(self):\n\
self.value = ''\n\
def write(self, txt):\n\
self.value += txt\n\
catchOutErr = CatchOutErr()\n\
sys.stdout = catchOutErr\n\
sys.stderr = catchOutErr\n\
"; //this is python code to redirect stdouts/stderr
Py_Initialize();
PyObject *pModule = PyImport_AddModule("__main__"); //create main module
PyRun_SimpleString(stdOutErr.c_str()); //invoke code to redirect
PyRun_SimpleString("print(1+1)"); //this is ok stdout
PyRun_SimpleString("1+a"); //this creates an error
PyObject *catcher = PyObject_GetAttrString(pModule,"catchOutErr"); //get our catchOutErr created above
PyErr_Print(); //make python print any errors
PyObject *output = PyObject_GetAttrString(catcher,"value"); //get the stdout and stderr from our catchOutErr object
printf("Here's the output:\n %s", PyString_AsString(output)); //it's not in our C++ portion
Py_Finalize();
return 0;
}
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