Question: I've been seeing some examples of Python being used with c++, and I'm trying to understand why would someone want to do it. What are the benefits of calling C++ code from an external language such as Python?

I'd appreciate a simple example - Boost::Python will do

Answer: 
Generally, you'd call C++ from python in order to use an existing library or other functionality. Often someone else has written a set of functions that make your life easier, and calling compiled C code is easier than re-writing the library in python.

The other reason is for performance purposes. Often, specific functions of an otherwise completely scripted program are written in a pre-compiled language like C because they take a long time to run and can be more efficiently done in a lower-level language.

A third reason is for interfacing with devices. Python doesn't natively include a lot of code for dealing with sound cards, serial ports, and so on. If your device needs a device driver, python will talk to it via pre-compiled code you include in your app.
Here's a real-life example: I've written a DLL in C to interface with some custom hardware for work. Then for the very first stage of testing, I was writing short programs in C to verify that the different commands were working properly. The process of write, compile, run took probably 3-5 times as long as when I finally wrote a Python interface to the DLL using `ctypes`.

Now, I can write testing scripts much more rapidly with much less regards to proper variable initialization and memory management that I would have to worry about in C. In fact, I've even been able to use unit testing libraries in Python to create much more robust tests than before. Would that have been possible in C? Absolutely, but it would have taken me much longer, and it would have been many more lines of code. 

Fewer lines of code in Python means (in general) that there are fewer things with my main logic that can go wrong.

Moreover, since the hardware communication is almost completely IO bound, there's no *need* to write any supporting code in C. I may as well program in whatever is fastest to develop.

So there you go, real-life example.