Accessing C++ Library from Python Code

[New! PyBind11 example added!]

This repo demonstrats how we can use a C++ library from Python by generating a Cpp shared object. This can be done directly by adding a few extra flags in gcc, or using setuptools library provided in Python. The later is a much cleaner approach. We can also use PyBind11, which simplifies the process greatly!

New: Added support for passing function pointer! See performOp() function in mygraph.py

The Cpp library is a simple Graph class that creates adjacency matrix dynamically through constructor. It also has other utility functions for printing the graph, setting edge, and freeing/disposing the dynamic memory.

Compile the shared object using gcc.

1. Run the following commands to generate shared object from mygraph.cpp file (or just run the make command).

• g++ -c -fPIC mygraph.cpp -o mygraph.o

• g++ -shared -Wl,-soname,libmygraph.so -o libmygraph.so mygraph.o

  Note: Conventionally, the generated shared object file's name starts with lib.

2. Run test.py to check if the graph is being used correctly (or just run the make test command). The mygraph.py works as a wrapper for the cpp library.

Compile the shared object through Python setuptools

1. Run the following command to generate shared object from mygraph.cpp file (or just run the make command). It will be generated in \build\*\ folder. In this case, the name of the shared object is automatically generated.

• python3 setup.py build or
• python setup.py build or
• py setup.py build

2. Run test.py to check if the graph is being used correctly (or just run the make test command). The mygraph.py works as a wrapper for the cpp library.

[New!] Compile the shared object through PyBind11 - to support C++11 features

1. Make sure that you have PyBind11 installed (pip install pybind11).
2. Run ./make.sh
3. Run python3 test.py or python test.py

Read the PyBind11 Documentation for more functionalities:

• https://pybind11.readthedocs.io/en/stable/classes.html
• https://pybind11.readthedocs.io/en/stable/advanced/functions.html
• https://pybind11.readthedocs.io/en/stable/advanced/classes.html

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Special thanks to the following tutorials

• https://nesi.github.io/perf-training/python-scatter/ctypes
• https://www.auctoris.co.uk/2017/04/29/calling-c-classes-from-python-with-ctypes/
• https://gist.github.com/Nican/5198719
• https://princekfrancis.medium.com/passing-a-callback-function-from-python-to-c-351ac944e041

Read More: https://tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html