pep8 design changes

```
setup_mac.py:47:57: E226 missing whitespace around arithmetic operator
setup_mac.py:61:1: E265 block comment should start with '# '
setup_mac.py:62:1: E265 block comment should start with '# '
setup_mac.py:71:3: E124 closing bracket does not match visual indentation
setup_mac.py:74:65: E231 missing whitespace after ':'

run_tests.py:62:1: E302 expected 2 blank lines, found 1
run_tests.py:84:35: E261 at least two spaces before inline comment
run_tests.py:90:80: W292 no newline at end of file
```
> Does this make the slice more readable?

I think the current version without spaces is fine. However, if the code in the slice were to become more complicated, it should be moved into a separate assignment where normal rules (spaces around operators) can apply.