Issue #142: CredentialField Python 3 fix

[apragacz]

This PR should fix issue #142.

Changes

• in oauth2client.django_orm.CredentialsField:
  • Python 2/3 metaclass support
  • using get_prep_value instead of get_db_prep_value
  • added value_to_string method
  • explicit conversions to text/bytes types in get_prep_value, to_python (required by Python 3)
• in test_django_orm tests:
  • added explicit conversion to bytes so the tests can work on Python 3

[googlebot]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project, in which case you'll need to sign a Contributor License Agreement (CLA).

📝 Please visit https://cla.developers.google.com/ to sign.

Once you've signed, please reply here (e.g. I signed it!) and we'll verify. Thanks.

---

• If you've already signed a CLA, it's possible we don't have your GitHub username or you're using a different email address. Check your existing CLA data and verify that your email is set on your git commits.
• If you signed the CLA as a corporation, please let us know the company's name.

[apragacz]

I signed it!

[googlebot]

CLAs look good, thanks!

[dhermes]

@nathanielmanistaatgoogle Here are the docs for smart_bytes and smart_text:

https://docs.djangoproject.com/en/1.8/ref/utils/#django.utils.encoding.smart_bytes (behaves like our _helpers._to_bytes)
https://docs.djangoproject.com/en/1.8/ref/utils/#django.utils.encoding.smart_text (behaves like our _helpers._from_bytes)

[dhermes]

Also worth noting this fixes the Python3 issues with metaclasses, previously attempted in #227 and it looks like this fixes #168 (in addition to #142, where the conversation with @szopu started).

@nathanielmanistaatgoogle Should we also have him fix class FlowField(models.Field) to work in Python3.

[apragacz]

@dhermes Done. Added the docstring & additonal tests. I decided that low-level testing of value_to_string should be enough.

[dhermes]

I wanted to make sure we don't introduce newly untested code paths.

We did not. After this PR, the only remaining untested parts are

• the django_orm.Storage class (100% untested, even constructor)
• the FlowField.to_python() method (has two uncovered branches)
• the FlowField.get_db_prep_value() method (has one uncovered branch)

All of these were untested before (and not part of this PR), so that's a good thing!

---

You can verify (as I did with these links to the untested lines).

Before this PR, the untested code paths are

https://github.com/google/oauth2client/blob/af6d3eb8067d5c95fb59af6fb62a192e6c7fa16b/oauth2client/django_orm.py#L46
https://github.com/google/oauth2client/blob/af6d3eb8067d5c95fb59af6fb62a192e6c7fa16b/oauth2client/django_orm.py#L48
https://github.com/google/oauth2client/blob/af6d3eb8067d5c95fb59af6fb62a192e6c7fa16b/oauth2client/django_orm.py#L53
https://github.com/google/oauth2client/blob/af6d3eb8067d5c95fb59af6fb62a192e6c7fa16b/oauth2client/django_orm.py#L71
https://github.com/google/oauth2client/blob/af6d3eb8067d5c95fb59af6fb62a192e6c7fa16b/oauth2client/django_orm.py#L73
https://github.com/google/oauth2client/blob/af6d3eb8067d5c95fb59af6fb62a192e6c7fa16b/oauth2client/django_orm.py#L78
https://github.com/google/oauth2client/blob/af6d3eb8067d5c95fb59af6fb62a192e6c7fa16b/oauth2client/django_orm.py#L101-L104
https://github.com/google/oauth2client/blob/af6d3eb8067d5c95fb59af6fb62a192e6c7fa16b/oauth2client/django_orm.py#L112-L120
https://github.com/google/oauth2client/blob/af6d3eb8067d5c95fb59af6fb62a192e6c7fa16b/oauth2client/django_orm.py#L131-L140
https://github.com/google/oauth2client/blob/af6d3eb8067d5c95fb59af6fb62a192e6c7fa16b/oauth2client/django_orm.py#L145-L146

Now they are

https://github.com/szopu/oauth2client/blob/b6bb23f0559c48bfb229de09142f01ee612ae3d4/oauth2client/django_orm.py#L83
https://github.com/szopu/oauth2client/blob/b6bb23f0559c48bfb229de09142f01ee612ae3d4/oauth2client/django_orm.py#L85
https://github.com/szopu/oauth2client/blob/b6bb23f0559c48bfb229de09142f01ee612ae3d4/oauth2client/django_orm.py#L90
https://github.com/szopu/oauth2client/blob/b6bb23f0559c48bfb229de09142f01ee612ae3d4/oauth2client/django_orm.py#L113-L116
https://github.com/szopu/oauth2client/blob/b6bb23f0559c48bfb229de09142f01ee612ae3d4/oauth2client/django_orm.py#L124-L132
https://github.com/szopu/oauth2client/blob/b6bb23f0559c48bfb229de09142f01ee612ae3d4/oauth2client/django_orm.py#L143-L152
https://github.com/szopu/oauth2client/blob/b6bb23f0559c48bfb229de09142f01ee612ae3d4/oauth2client/django_orm.py#L157-L158

[dhermes]

This LGTM

@nathanielmanistaatgoogle are we a go to merge this?

---

After merging, someone (I can do it) needs to update django_orm.FlowField to also be Python3 compatible (modeled after this PR) and then add tests for it (that PR might as well also add tests for django_orm.Storage).

[nathanielmanistaatgoogle]

Looks mergeable to me; thank you for leading review!

[dhermes]

Thanks @szopu !