[boto] Default to None if no region

[Kyle-Verhoog]

Fixes #525, also applies formatting.

[palazzem]

One change in the meta list. Do we have a way to introduce a test to avoid a regression?

[palazzem]

with the None default, get_region_name(region) returns None. Maybe we should add aws.region tag only if it's not none?

[Kyle-Verhoog]

I'd prefer this behaviour, but I opted to stay consistent with the functionality of line 143:

dd-trace-py/ddtrace/contrib/boto/patch.py

Line 143 in 56cb63f

region = getattr(instance, "region", None)

[Kyle-Verhoog]

This will result in the region tag showing up as 'None', which isn't ideal. Let's not add it if it's none.

[palazzem]

exactly, let's not add it if it's None

[Kyle-Verhoog]

Giving it a quick look, the moto library we use to mock boto doesn't seem to allow us to mock the region not being set. Creating a regression test would require a non-trivial amount of work.

[palazzem]

can you move these as a constants? better in a constants.py module. So they're all in one place + you use the same variable in 2 parts of the code

[SeanOC]

Looks good. Probably would be good to queue a follow-up task to make an upstream patch to moto to allow region to be empty and then provide a test here.