I was talking to a fellow Python enthusiast the other day, and the topic came up of Python's great dynamic nature. I said that I didn't think it had had that big an effect on me. He was surprised. "You don't like dynamic typing?" he asked. It's not that. Looking back over my experience with Python, it's not the dynamic typing that has affected me most. Let me explain:
Python fits my expectations: the dynamic typing was simply what my primitive monkey coding brain expected. There's a strong contrast to C++'s static-typing friction, and include file hell, but because of my mental expectations, that contrast feels like a point taken from C++, not a point given to Python.
When working in C++, the Python thing I miss more than dynamic typing are the easy to use built-in data types like lists and dictionaries. The amount of noise you have to introduce into your code when using the STL is just staggering. It's a true impediment to progress. Let's say I have an A and want a B, and there's a simple mental path between the two (string to split array, array to joined string, and so on). In Python (and most other "scripting" languages), it's a simple expression that makes sense. In C++ or Java, it's three or four lines of idiomatic yet still not memorizable code. I find myself having to go and find the last place I did it in the code, and copying.
Also, I haven't yet used a lot of Python's deeper mysteries: metaclasses, decorators, and so on. I've benefited from them in other people's code (like SQLObject's magic), but I haven't made use of them myself. I've built much larger systems in C++ and Java than I have in Python, so I haven't yet needed some of the raw power in Python.
But if I had to pick the biggest effect Python has had in me as a programmer, it's been about testing. My experience writing automated tests in Python projects is that I am freed from fear. I don't have to worry about forgotten corners of the code. I've tried to apply that mind set in non-Python projects. The change in philosophy about testing is a much bigger change in me because I can apply it outside of Python. I wrote code differently, and approach development differently. And I can use those concepts in C++ code, whereas dynamic stuff is left behind with the Python.
So no, Python's dynamic nature is not its defining characteristic for me. And to be perfectly honest, I have a lot of static typing habits that I'm still trying to break.