How To catch python stdout in c++ code(如何在 C++ 代码中捕获 python 标准输出)
问题描述
我有一个程序,它在运行期间有时需要调用 python 来执行某些任务.我需要一个函数来调用 python 并捕获 python 标准输出并将其放入某个文件中.这是函数的声明
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)
我的问题是捕获给定命令的所有 python 输出 (pythonInput).我没有使用 python API 的经验,我不知道什么是正确的技术来做到这一点.我尝试的第一件事是使用 Py_run_SimpleString 重定向 python 的 sdtout 和 stderr这是我编写的代码的一些示例.
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 "boostpython.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;
}
有没有更好的方法来做到这一点?此外,由于某些原因,PyRun_SimpleString 在得到一些数学表达式时什么也不做,例如 PyRun_SimpleString("5**3") 什么都不打印(python conlsul 打印结果:125)
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)
也许这很重要,我正在使用 Visual Studio 2008.谢谢,亚历克斯
maybe it is important, i am using visual studio 2008. Thanks, Alex
我根据 Mark 的建议所做的更改:
Changes I've made according Mark's suggestion:
#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
"; //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
", 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:
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
这对我有好处,但只有一个问题,应该是
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
我不知道为什么但是在运行这个命令之后:PythonPrinting("1+5"), PyString_AsString(output) 命令返回一个空字符串 (char*) 而不是 6... :( 有什么我不能做的吗?松开这个输出?
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?
谢谢,亚历克斯
推荐答案
如果我正确阅读了您的问题,您想将 stdout/stderr 捕获到 C++ 中的变量中吗?您可以通过将 stdout/stderr 重定向到一个 python 变量,然后将该变量查询到您的 C++ 中来做到这一点.请注意,我没有在下面进行正确的引用计数:
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
class CatchOutErr:
def __init__(self):
self.value = ''
def write(self, txt):
self.value += txt
catchOutErr = CatchOutErr()
sys.stdout = catchOutErr
sys.stderr = catchOutErr
"; //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:
%s", PyString_AsString(output)); //it's not in our C++ portion
Py_Finalize();
return 0;
}
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本文标题为:如何在 C++ 代码中捕获 python 标准输出
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