Safe qt importer

[fdan]

If the tank authentication is used in a headless mode, it will raise an unhandled exception as shown below.

Using the get method to retrieve modules in qt_importer.py will avoid the index error and is also just simpler.

  File "/foobar/pipeline/config/studio/install/core/python/sgtk/__init__.py", line 16, in <module>
    import tank
  File "/foobar/pipeline/config/studio/install/core/python/tank/__init__.py", line 110, in <module>
    from . import authentication
  File "/foobar/pipeline/config/studio/install/core/python/tank/authentication/__init__.py", line 35, in <module>
    from .shotgun_authenticator import ShotgunAuthenticator
  File "/foobar/pipeline/config/studio/install/core/python/tank/authentication/shotgun_authenticator.py", line 13, in <module>
    from .sso_saml2 import has_sso_info_in_cookies, has_unified_login_flow_info_in_cookies
  File "/foobar/pipeline/config/studio/install/core/python/tank/authentication/sso_saml2/__init__.py", line 15, in <module>
    from .core.errors import (  # noqa
  File "/foobar/pipeline/config/studio/install/core/python/tank/authentication/sso_saml2/core/__init__.py", line 15, in <module>
    from .sso_saml2_core import SsoSaml2Core  # noqa
  File "/foobar/pipeline/config/studio/install/core/python/tank/authentication/sso_saml2/core/sso_saml2_core.py", line 46, in <module>
    from .username_password_dialog import UsernamePasswordDialog
  File "/foobar/pipeline/config/studio/install/core/python/tank/authentication/sso_saml2/core/username_password_dialog.py", line 27, in <module>
    from ...ui.qt_abstraction import QtCore, QtGui
  File "/foobar/pipeline/config/studio/install/core/python/tank/authentication/ui/qt_abstraction.py", line 22, in <module>
    QtWebEngineWidgets = _importer.QtWebEngineWidgets
  File "/foobar/pipeline/config/studio/install/core/python/tank/util/qt_importer.py", line 89, in QtWebEngineWidgets
    return self._modules["QtWebEngineWidgets"]```

[halil3d]

The previous syntax implies self._modules may not be set when called so you may need this instead:

Suggested change

	return self._modules.get("QtCore")
	return self._modules.get("QtCore") if self._modules else None

This covers QtCore or the module not being present in the dict and the dict itself not being set.

[fdan]

If the _modules dict is initialised to an empty dict, get should still be safe, i.e.

>>> d = {}
>>> print(d.get('foobar'))
None

If the issue is covering a scenario where _modules is not an attr of the object at all, I don't think we'd need to do that as it's in the constructor?

[staceyoue]

I would prefer the suggestion by @halil3d above, instead of initializing self._modules in the constructor to an empty dictionary, because for a couple of minor reasons:

1. If _modules is None, this clearly indicates that the import failed for the requested Qt interface. An empty dict may suggest a different error during the import.
2. The modules property returns the the value of _modules - so we would be changing the return value from None to {} if the import failed. Which means if callers are checking specifically for None, this would break their code.

[staceyoue]

LGTM - just one minor comment.

[staceyoue]

I would prefer the suggestion by @halil3d above, instead of initializing self._modules in the constructor to an empty dictionary, because for a couple of minor reasons:

1. If _modules is None, this clearly indicates that the import failed for the requested Qt interface. An empty dict may suggest a different error during the import.
2. The modules property returns the the value of _modules - so we would be changing the return value from None to {} if the import failed. Which means if callers are checking specifically for None, this would break their code.