Selected yaml.Loader while reading odml documents

[Aniket-Pradhan]

Fixes #343 .

Selecting a PyYaml loader instead of the default loader. The default loader fails on Python 3.8

[coveralls]

Coverage increased (+0.02%) to 75.129% when pulling 48e55a2 on Aniket-Pradhan:master into 3ebada5 on G-Node:master.

[Aniket-Pradhan]

Ach... Sorry for the delay...

I am not sure if the coding style is fine or not. I'll wait for the tests and resolve them if there is any problem

[achilleas-k]

Hi. Thanks for the PR. This is great.

I haven't looked at everything in detail yet, but the test failures are all for Python 2.7. Now, given the EOL status of Python2, we are planning on dropping support sometime soon. However, since we haven't yet decided exactly which release will be the last Python2-compatible one, I think we would want this fix to be compatible with both 3 and 2.

Can you have a look at the issue and add it to the fix?

[achilleas-k]

Looks good. Small formatting issue with indentation.

Also, we should probably add the same change with the Loader to yaml.load() on L181 in the from_string() method.

[Aniket-Pradhan]

Python 2 version of PyYaml seems to lack a constructor to load Unicode values by default using the SafeLoader (I don't know why... since the library is the same for Python 3 as well). I have added in a constructor to alleviate the problem, however, this problem exists only for Python 2 and hence the solution applies to Python 2 only. The constructor---in my assumption, should have no effect on Python 3 installations.

We can also revert from using the SafeLoader to Loader itself, but I do not think it is worth the risk, and the given warning from the PyYaml team.

[achilleas-k]

Hey. Thanks again.

I think yaml.load() in the from_string() method should also use the SafeLoader for the same reasons.

[Aniket-Pradhan]

You're right.

I completely missed that loader. Fixing it.

Anyhow, I was also looking at yaml.safe_dump, but it cannot represent arbitrary python objects (datetime.date), therefore we cannot use it unless the devs fix the datetime.date and datetime.time inconsistency.

[EDIT]: Rebased and force pushed to squash small commits to one big commit.