Something insane I did not know about python

insane.py

H:\temp>python
Python 2.7.11 (v2.7.11:6d1b6a68f775, Dec  5 2015, 20:32:19) [MSC v.1500 32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> a = 'hello'
>>> print a
hello
>>> words = [a for a in ['one', 'two', 'three']]
>>> print words
['one', 'two', 'three']
>>> print a
three
>>>

I can understand mechanically why it does that, but that was really unexpected to me. I always assumed the list comprehension like feature would introduce a new scope where the variables would live.

It basically treats the [a for a in [...]] syntax just as sugar for a surrounding for loop, which trashes the other variable

for a in [...]:

Yeah that's fun. Basically only def and class introduce scopes, nothing else (I think). The behavior above is sort of a feature since you can search for something in a loop and access it after.

And then you're like "what if I get to the end of a loop and nothing matched?" To counteract that for loops can have an "else" clause. :)

The 90's were weird.

Yeah this reminds me a lot of JavaScript. I thought python had more scopes.. I guess I'll liberally enclose most of my scopes in local functions from now on, unless it's at the expense of clarity