Use Python idioms in source

Typically, you do one import per line and do system modules first, then installed third-party modules, then local modules [per PEP 8](http://legacy.python.org/dev/peps/pep-0008/#imports).

Doing raw path manipulation is discouraged as well, the [`os.path` module](https://docs.python.org/2.7/library/os.path.html#module-os.path) has functions to do it for you cleanly.

Finally, you can send a list of arguments to a function and auto-unpack them:

    vals = (a, b, c)
    f(*vals)

is the same as:

    f(a, b, c)

and then you don't have to think about it if you add a column later.