Remove redundant pass-es.
Remove unused variable (idx).
Enforce new-style capturing of exception object (PEP 3110).
Invoke join on separator.
Remove unused import.
Replace calls to map with list comprehensions.

In Python 2, a call to `map` builds an actual list,
so it behaves exactly the same as the comprehension syntax.
The latter reads better.
Replace one-off lists with generators.

As the entire list doesn't get built, less space is needed
and performance may improve.
Switch empty order messages
Drop unnecessary slice.
Fix typos.
Remove unused import.
Merge pull request #534 from Renelvon/style_fixes

Style fixes
Merge pull request #533 from hoffmabc/master

Switch empty order messages