How to compile my project so it can be used from python? I've read that I should create a *.so file but how to do so?

That depends on your compiler. By example with g++: g++ -shared -o myLib.so myObject.o

Should it work like a lib, so python calls some specific functions, chosen in python level?

Yes it is, in my opinion. It seems do be the "obvious" way, since it's great for the modularity and the evolution of the C++ code.

Here is an example using SWIG:

The Python code which calls C++ function "inflow":

 import inflow    # importing C++ inflow library
 nframes = 25
 print 'calling inflow function in loop ...'
 for i in xrange(0,1001):
      z = inflow.inflow(""" arguments""")
     """ code does something with z """

The C++ function will be as usual:

 #include <iostream>
 #include <vector>
  inflow(/* arguments from Python*/)
  {
   /* code does something */

  }

Now to interface with Python, here are the steps:

1) IMPORTANT - Make sure the C++ code you are trying to bind in this step has a different name than the one given in the command. Else it will overwrite with swig code.

Lets say example_wrap.cpp is the file you want to interface with Python and "example.i" is the SWIG interface file. SWIG will generate a new file with the name example.cpp.

2) swig -c++ -python -o example_wrap.cpp example.i

3) g++ -I /usr/include/python2.7 -fPIC -c example_wrap.cpp -o example_wrap.o

4) g++ -shared -o _example.so example_wrap.o

Idea is that the compiled module name should start with an underscore, followed by the name.

5) Open Python in term, and say

from example import *

and then start calling the functions.

6) Source : http://www.iram.fr/~roche/code/python/SWIG.html#purpose

The interface file for the example would look something like this:

 %module example
 %{
   #include "example.h"
 %}

 %include "std_vector.i"
 // Instantiate templates used by example
 namespace std {
  %template(IntVector) vector<int>;
  %template(DoubleVector) vector<double>;
  }

  // Include the header file with above prototypes
  %include "example.h"

1. I think you should take a look in boost python, it's an amazing library and also works in linux, windows and mac. Using boost python, you can export your classes and functions in order to access them directly from python. There are many many examples and the documentation is very good!!!

2. Using boost python, you should define which functions/classes you want to expose, and them compile your source code into a library file that's going to be imported inside python.

The Simple, Effective, and Quick Approach:

Void Methods

test.cpp

#include <iostream>
extern "C" void Print()
{
    std::cout << "This is data from inside a c++ file." << std::endl;
}

Compile time commands

g++ -c -fPIC test.cpp -o test.o // DO NOT FORGET '-fPIC'
g++ -shared -o test.so test.o // FOR UNIX ONLY

Main.py

from ctypes import cdll

test = cdll.LoadLibrary('./test.so')
test.Print()

Passing and returning values

In test.cpp

extern "C" int Multiply(int a, int b)
{
    return a*b;
}

In Main.py from ctypes import cdll

test = cdll.LoadLibrary('./test.so')
value = test.Multiply(5,5)
print(value)

Summary
No additional libraries are needed.
No constructors are needed.
No c++ classes are needed.
No public declarations are needed.

Simply create a method and mark it as extern "C"
Then call it in python.