All languages used in web server that don't spawn a new process for each request have the same feature.
It's trivial to have a single-process JS application with multiple JS global objects in it. Case in point: any web browser (and renderer processes don't change this: every iframe on a page has a separate global object).
It's just that Node _chose_ to reuse the same global object for multiple requests instead of using a clean execution environment.
I have to agree with jessedhillon: that sounds insane.
Even without doing this experiment, the result is obvious. There would have to be some meta process to start new interpreter processes here in order to prevent the same environment from being reused. Since that is not the case, because you have to invoke the python interpreter manually here, you cannot get multiple distinct results.
(Theoretically, in this code, you could get two different responses if they both entered the `if ... is None` clause in send_head() before one of the requests could cause the global variable to be set.)
In the case of Node, it's embedding V8. It can in fact run JS code of its choice in an environment of its choice, set up new globals, etc.
In practice, this problem is why you see `Array.isArray`, `jQuery.isArray`, `_.isArray` and friends so often -- they exist to give a canonical, non-"check if any member of X's inheritance chain matches Y.prototype" way to determine if a given instance is actually an array.
So, in summation: yes, it's weird that Node has this, but ultimately it's a lesser-vilified problem of JavaScript's.
[0]: https://github.com/joyent/node/blob/master/lib/module.js#L51 -- `NODE_MODULE_CONTEXTS=1 node <file.js>` will run separate modules in separate global contexts.