When we want to get something done, we typically reach for what is most familiar.
I probably gave the most chance to Common Lisp. It's a very pragmatic language too, unfortunately (largely for historical reasons), the standard library didn't keep the pace. It's not just a matter of what you can do, it's also the design. Python standard libraries almost always put the user first and the purity second.
For instance, Python would never add versions of functions remove-if, remove-if-not, delete-if, delete-if-not. That's mathematical purity (in if vs. if-not) and letting the onus of choice on user (in delete-if vs. remove-if) instead of conservatively making reasonable default.
At the same time, Common Lisp library lacks things like function to strip whitespace from string; you can do it, but Python has it as a function. It's just hundreds of little things like these that make Python more pleasant to work with.
I genuinely want to like Lisp more than Python (I am learning Clojure about now, which is on par with Common Lisp when it comes to pragmatism). But sometimes it is just a little more frustrating, because of ideology and not putting user first when it comes to API design.
I'm sure there are better solutions to that though, and I never got around to actually generating the validators.
This does not apply to Python, however. It does have a explicit, if not entirely serious, statement of its ideology in The Zen of Python. (For those unfamiliar, read http://c2.com/cgi/wiki?PythonPhilosophy. It has The Zen and some discussion.) Python takes its ideology pretty seriously, too, as evidenced by how much the words "pythonic" and "unpythonic" used in discussions involving the language. In discussions around, e.g., Java you will find no terms of that sort.
The thing is these rules do not really give much guidance on how to design a programming language. These don't hint whether or not the language should be functional, or should have small library, or should have classes, and bazillion other things that programming language designers tend to argue about.
We can pretty much agree on these rules. And that's the point, these rules are all about making tradeoffs.