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
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.
Practical point of view: Why would I want to use Python with C++?