Avoid loading python-ecdsa when using the cryptography backend

[bdraco]

In #117 dependency on ecdsa cryptography backend was removed, however it is still loaded even when not used. Since ecdsa has a load time performance penalty when gmpy2 is not installed, this can be a bit painful on embedded systems.

We can avoid all this overhead and check to see if the key object hasattr to_pem instead since we only
care of these if ecdsa has already been loaded by something else.

[bdraco]

The test failure is unrelated and documented here : #176

[blag]

Thanks for this, I like it. I'm waiting on tlsfuzzer/python-ecdsa#205 to be merged, but in the meantime would you mind pinning ecdsa < 0.15 in requirements.txt so the tests pass for this PR? Once the tests pass I'll merge it in.

[blag]

I have another branch that I'm actively working on where I make the Travis tests a lot more straightforward, so this should hopefully not be an issue for very much longer, but for now the Travis configuration hands off to tox to run the actual tests.

And tox "installs the current package", which seems to mean that it runs the equivalent of python setup.py install. Unfortunately, none of that machinery reads requirements.txt, so only pinning ecdsa there won't fix the tests (it does fix installation via pip though). You'll have to tweak the constraints in legacy_backend_requires in setup.py to fix the tests.

[codecov]

Codecov Report

Merging #178 into master will decrease coverage by 6.31%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #178      +/-   ##
==========================================
- Coverage   97.18%   90.87%   -6.32%     
==========================================
  Files          14       14              
  Lines        1067     1063       -4     
==========================================
- Hits         1037      966      -71     
- Misses         30       97      +67     

Impacted Files	Coverage Δ
jose/backends/cryptography_backend.py	98.07% <100.00%> (-0.04%)	⬇️
jose/backends/rsa_backend.py	60.27% <0.00%> (-36.31%)	⬇️
jose/utils.py	69.56% <0.00%> (-30.44%)	⬇️
jose/backends/__init__.py	81.81% <0.00%> (-18.19%)	⬇️
jose/backends/pycrypto_backend.py	97.52% <0.00%> (+1.65%)	⬆️

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[bdraco]

@blag I'm not sure what is going on with codecov here 🤷‍♂️ , but the change has 100% of diff hit.

[blag]

No worries, codecov gets confused sometimes. This looks good. Thank you for fixing the tests and dependency!

[bdraco]

Thanks @blag. Can we get a version bump so we can get this in Home Assistant release 0.114?

[blag]

Wow, you all really seem to take "release early, release often" as "release right now, release constantly". 😜

I'll bump the version and publish it to PyPI. Thank you all for Home Assistant!

[blag]

@bdraco Version 3.2.0 is now available on PyPI and GitHub. 😄

[bdraco]

@bdraco Version 3.2.0 is now available on PyPI and GitHub. 😄

Thank you 🍾