PEP8 fixes and code clarity

Mostly PEP8 fixes, a removal of a stale code comment on dict comprehension and a minor 'if not' statement fix.

## PEP8
+ PEP8 correction; "block comment should start with '# '"
+ Indented comment to match block
+ Keeping line number under 79 chars

## Code clarity
Remove redundant TYPE_CHOICES dict comprehension, Python 2.7 doesn't have dictionary comprehension.
Put the multiline comment in a variable to satisfy PEP8, it's not as performant (i.e. a variable is allocated unecessarily) but it's readable.