conversion.py: Draft basic cleanup - UNTESTED

[schwehr]

I haven't tested these changes. Without unit tests, I would not trust these changes.

The goal was to capture some initial cleanups that can be done on this file.

Changes:

• Remove commented out code
• Simplify use_math()
• Remove unnecessary variables if just returning a value
• Move code out of with open() scopes
• x = x + foo → x += foo
• No need to test a list to make sure it's not None if files is not None:
• Comprehensions can be done right on results of a glob

There is a lot more than can be done (like making most of this code totally isolated from Jupyter), but this is a start.

An easy starter unit test:

class ConversionTest(unittest.TestCase):

  def test_use_math(self):
    self.assertFalse(conversion.use_math(['math', 'mATH']))
    self.assertTrue(conversion.use_math(['a', 'Math.pow()']))

[giswqs]

This conversion module has changed significantly in #1968. There are several merge conflicts now. Sorry.

[schwehr]

No worries. This was meant more to document ideas than to be a PR that is merged.