SDK namespace package

[c24t]

This PR adds a stub tracer implementation that depends on the API.

Doing this required some package surgery: moving the opentelemetry package in opentelemetry-api to opentelemetry.api and losing opentelemetry/__init__ modules, making both API and SDK PEP 420 namespace packages.

The result is that you can now install both packages without either clobbering the other and causing import errors.

@reyang let me know if this matches your grand vision for the package structure.

[c24t]

Setting PYTHONPATH instead of installing the package was a kludge. It may be possible to get mypy to pass without setting MYPYPATH here, but just installing the packages didn't seem to do it.

[c24t]

We may not want separate test targets in the long run, but this was the easiest way to get test discovery to work since opentelemetry isn't a package (with an __init__.py) anymore.

[reyang]

We want to remove opentelemetry/__init__.py after we workaround the pylint discovery issue #37 (comment).

[c24t]

It would be better to install these as regular deps so they're not reinstalled on each run. There may be another better way to do this.

[c24t]

See python/mypy#1645, mypy fails to find opentelemetry.api without this flag.

[reyang]

This is different from my understanding. We've discussed that given users are only going to use APIs in their code, it makes more sense to let them use import opentelemetry.trace.foobar instead of import opentelemetry.api.trace.foobar. Maybe I've missed something, which problem did you see @c24t?

Regarding the __init__.py file, it was a temporary thing to unblock tox #37 (comment), would be great to get it removed.

With what we have in the master branch today, installing/uninstall api/sdk package should work:

E:\opentelemetry-python\opentelemetry-api>pip install .
Processing e:\opentelemetry-python\opentelemetry-api
Building wheels for collected packages: opentelemetry-api
  Building wheel for opentelemetry-api (setup.py) ... done
  Stored in directory: C:\Users\reyang\AppData\Local\pip\Cache\wheels\53\5b\1f\5953c7ce944056c8b8062b53185672010c9b07d8bf8b83d62e       
Successfully built opentelemetry-api
Installing collected packages: opentelemetry-api
Successfully installed opentelemetry-api-0.1.dev0

E:\opentelemetry-python\opentelemetry-api>cd ..\opentelemetry-sdk

E:\opentelemetry-python\opentelemetry-sdk>pip install .
Processing e:\opentelemetry-python\opentelemetry-sdk
Building wheels for collected packages: opentelemetry-sdk
  Building wheel for opentelemetry-sdk (setup.py) ... done
  Stored in directory: C:\Users\reyang\AppData\Local\pip\Cache\wheels\49\57\d1\0faf86eb968fb8959880eea93f73520d53b073de7316e7192a       
Successfully built opentelemetry-sdk
Installing collected packages: opentelemetry-sdk
Successfully installed opentelemetry-sdk-0.1.dev0

E:\opentelemetry-python\opentelemetry-sdk>pip uninstall opentelemetry-sdk
Uninstalling opentelemetry-sdk-0.1.dev0:
  Would remove:
    c:\python37\lib\site-packages\opentelemetry\sdk\*
    c:\python37\lib\site-packages\opentelemetry_sdk-0.1.dev0.dist-info\*
Proceed (y/n)? y
  Successfully uninstalled opentelemetry-sdk-0.1.dev0

E:\opentelemetry-python\opentelemetry-sdk>pip uninstall opentelemetry-api
Uninstalling opentelemetry-api-0.1.dev0:
  Would remove:
    c:\python37\lib\site-packages\opentelemetry\*
    c:\python37\lib\site-packages\opentelemetry_api-0.1.dev0.dist-info\*
Proceed (y/n)? y
  Successfully uninstalled opentelemetry-api-0.1.dev0

[c24t]

The problem is that the API package takes over the opentelemetry namespace:

% pip install -e opentelemetry-sdk; python -c "from opentelemetry import sdk"
Obtaining file:///Users/libc/src/opentelemetry-python/opentelemetry-sdk
Installing collected packages: opentelemetry-sdk
  Running setup.py develop for opentelemetry-sdk
Successfully installed opentelemetry-sdk
% pip install -e opentelemetry-api; python -c "from opentelemetry import sdk"
Obtaining file:///Users/libc/src/opentelemetry-python/opentelemetry-api
Installing collected packages: opentelemetry-api
  Running setup.py develop for opentelemetry-api
Successfully installed opentelemetry-api
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ImportError: cannot import name 'sdk' from 'opentelemetry' (/Users/libc/src/opentelemetry-python/opentelemetry-api/src/opentelemetry/__init__.py)

[reyang]

This is due to the fact that we haven't removed opentelemetry/__init__.py.
Once we workaround the pylint discovery issue, we're good to remove opentelemetry/__init__.py, then the namespace package will work.

[c24t]

Got it, removed the api package in 2b527fb. Having separate API and SDK test targets seems like a good solution in the meantime.

[reyang]

LGTM