ipycpp

Simple and hackable jupyter kernel for running c++ (c plus plus) codes inside a python notebook.

Rather than providing a true interactive experience, this kernel would just extract the cpp code from the notebook, compile it on the fly and print the result. It is meant as a drop-in replacement for your main cpp file.

Install with:

pip install ipycpp

The package itself is in pure python, and will just call the cpp compiler already installed in your system. Of course, you have to provide a suitable cpp compiler, such as g++ in order to make it work. Advanced build tools such as make should work as well.

Motivation

Other packages, such as xeus-cling provide a better interactive experience when working with cpp, yet they introduce a lot of magic behind the scene. While developing algorithms with cpp, you usually care more about speed and low level control. This package guarantees no overhead - it just transpiles your notebook into a plain .cpp file: you may even check the result by yourself. Moreover, since this package is just a ~300lines pure python script, it's way easier to setup.

Usage

Note: you may find a complete example here, example.ipynb

First, you have to provide some configuration.

• $$ipycpp_file: this is the location where your code would be extracted
• $$ipycpp_build: this is the command ipycpp should use to compile your code
• $$ipycpp_run: this is the command ipycpp should use to compile your code

Create a cell with:

// $$ipycpp_file: src/main.cpp
// $$ipycpp_build: g++ src/main.cpp -o bin/main
// $$ipycpp_run: bin/main


/* you may also declare global variables and include directives */

#include <stdio.h>

auto hello = "hello world!";

Then, you may add other cells with some shared functions, for example:

void printHelloWorld(){
	printf("%s\n", hello);
}

Finally, when you want to show some output value, you may declare the usual main function, just remembed to surround it with the special #ifdef IPYCPP_MAIN guard or use the "clevermain" mode (see below).

#ifdef IPYCPP_MAIN
#define IPYCPP_MAIN_METHOD
int main(){
	printHelloWorld();
}
#endif

Keep in mind that the notebook is stateless. Everything will be recompiled EVERY time. If you change a variable inside a main function and then run another cell, the change will be overwritten.

CleverMain mode

If you wish, you may ask ipycpp to automatically recognize your main methods. Use the // $$ipycpp_clevermain: true on your first cell instead of writing #ifdef IPYCPP_MAIN every time.

For example:

// $$ipycpp_file: src/main.cpp
// $$ipycpp_build: g++ src/main.cpp -o bin/main
// $$ipycpp_run: bin/main
// $$ipycpp_clevermain: true

#include <stdio.h>

auto hello = "hello world!";


int main(){
  	printf("%s\n", hello);
}

// another cell
int main(){
  	printf("another cell, %s\n", hello);
}

This works 99% of the times, but may incur into issues if you are doing some weird preprocessor magic (ipycpp has no way to resolve in advance your #define directives).

Special formatting

You may provide non-textual data to the notebook, such as html or images, by printing some special tags. This feature is enabled by default, and let you create interactive notebooks.

disable

To disable any kind of special data for the rest of the cell, just print $$$ipycppr_disable_special_output$$$ at the beginning of your main.

For example:

printf("$$$ipycppr_disable_special_output$$$\n");

In this way, you will be sure that any further output will be printed "as is".

images or other files

You may display an image (or another kind of file) by printing the special tag $$$ipycppr_file$$$ followed by the image path. ipycpp will guess the kind of file from the extension. For example:

printf("$$$ipycppr_file$$$%s\n", "myfolder/myimage.png");

html

Mark html regions with $$$ipycppr_html_start$$$ and $$$ipycppr_html_end$$$ (newline required). You may also add some javascript logic to create interactive widgets.

Basic example:

printf("$$$ipycppr_html_start$$$\n%s\n$$$ipycppr_html_end$$$\n", "<b>some bold text</b>");

Advanced example (this will create an interactive widget using the PetiteVue library; the widget will display a number and two buttons to increment or decrement it):

auto html = R""""(

<div class="widgetcontainer">
  <div class="widget" v-scope="{ count: 0 }">
    <button @click="count--">-</button>
    {{ count }}
    <button @click="count++">+</button>
  </div>

  <script>
  if(!window.INSTALL_PETITE_VUE){
    let resolve = null;
    window.INSTALL_PETITE_VUE = new Promise(r => resolve = r);
    function loadPetiteVue(){
      var script = document.createElement('script');
      script.src = 'https://unpkg.com/petite-vue';
      script.onload = resolve;
      script.onerror = () => setTimeout(loadPetiteVue, 1000)
      document.head.appendChild(script);
    }
    loadPetiteVue()
  }

  {
    // get current element right now, and mount it as soon as petite-vue is loaded
    let element = document.currentScript.previousElementSibling;
    window.INSTALL_PETITE_VUE.then(() => PetiteVue.createApp().mount(element));
  }

  </script>
</div>
)"""";

#ifdef IPYCPP_MAIN
#define IPYCPP_MAIN_METHOD
int main(){
	printf("$$$ipycppr_html_start$$$\n%s\n$$$ipycppr_html_end$$$\n", html);
}
#endif

Authors and license

Main author: Luca Fabbian luca.fabbian.1999@gmail.com

Freely distributed under MIT license.

Feel free to open a github issue to report bugs or submit feature requests!