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: 
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.
One nice thing about using a scripting language is that you can reload new code into the application without quitting the app, then making changes, recompile, and then relaunching the app. When people talk about quicker development times, some of that refers to this capability.
A downside of using a scripting languages is that their debuggers are usually not as fully featured as what you would have in C++. I haven't done any Python programming so I don't know what the features are of its debugger, if it has one at all.

This answer doesn't exactly answer what you asked but I thought it was relevant. The answer is more the pro/cons of using a scripting language. Please don't flame me. :)