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I want to call a python script from C++ and wish to use the output .csv file generated by this script back into C++. I tried this in main():

std::string filename = "/home/abc/xyz/script.py";
std::string command = "python ";
command += filename;
system(command.c_str());

This does call and execute the python script.

EDIT_2 The 'print' commands in the python are being executed...things are being printed on the screen when the script is called. So far so good. But! it is not creating the .csv file (part of the same script). like: i had a training.csv file with 100 entries. I called the python script, with little changes to the script so that the trainig.csv file now should contain only 50 entries instead of 100. Its overwritten. But, no such thing happening. Rest of the commands in script (print, etc) are working perfectly. The training.csv file is to be read with C++ normally using fstream and getline...

Any idea how to do it?

EDIT using linux

Thanks!

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2  
You may want to look at ways of embedding (and extending) python instead of dealing with invocations of the python interpreter via shell. –  Christian Kiewiet Jun 6 '13 at 12:47
2  
Depends on the platform. Windows and Unix have different approaches. Which are you on? And there's nothing Python specific about this. –  user9876 Jun 6 '13 at 12:47
2  
This should get you started: stackoverflow.com/questions/9405985/… –  StoryTeller Jun 6 '13 at 12:53
2  
Also, for shorter sample stackoverflow.com/a/478960/1715716 –  Gauthier Boaglio Jun 6 '13 at 12:58
1  
If the python script creates a csv file. Then you don't need to redirect the scripts output. Just run it, and open the file it created using the standard C++ api. –  StoryTeller Jun 6 '13 at 13:17

2 Answers 2

up vote 2 down vote

Try using POSIX's popen() instead of system(). It pipes stdin/stdout of child process to returned file handle.

FILE* in = popen(command.c_str(), "r");

fscanf(in, ... // or some other method of reading

pclose(in);
share|improve this answer
1  
You mean fscanf, me thinks :) –  StoryTeller Jun 6 '13 at 13:38
    
yep, corrected. –  Vovanium Jun 6 '13 at 13:40
    
@Vovanium not helping :( could you please show a sample...thanks! –  learner Jun 6 '13 at 14:07
up vote 0 down vote

Here is a solution to embed the execution of your python module from within your C++ application. It's not better or worst than forking/executing your python script through a system call, it just is a different way to do it. Whether it is best or not depend on your context and usage.

Some time ago I have coded a way to load python modules as plugins to a C++ application, here's the interesting part.

Basically, you need to #include <Python.h>, then Py_Initialize() to start your python interpreter.

Then you do import sys, using : PyRun_SimpleString("import sys");, and you can load your plugin by doing PyRun_SimpleString('sys.path.append("path/to/my/module/")').

To exchange values between C++ and Python, things get harder, you have to to transform all your C++ objects into python objects (starting line 69 in my script).

Then you can call your function using PyObject_Call_Object(...), using all the python objects you created as arguments.

You get the return value, and transforms all those values in C++ objects. And don't forget the memory management in all that!

To end your python interpreter, a simple call to Py_Finalize().

It really looks harder than it is really, but you have to be really careful doing this, because it could lead to leaks, security issues etc..

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thanks!!!! but wt to say....m kinda beginner.....dis all seems so nerdy stuff!!! :O :O :O –  learner Jun 6 '13 at 13:22

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