Default session for the TensorFlowModel

[ivust]

As I understood from the code (https://github.com/bethgelab/foolbox/blob/master/foolbox/models/tensorflow.py), the constructor of the TensorFlowModel tries to use the default session, otherwise it creates a new one, where all variables need to be reinitialised. That means that if there is a running session with initialised variables in it, then the TensorFlowModel should be created with this session being a default one:

with sess.as_default():
    model = foolbox.models.TensorFlowModel(...)

Maybe that is obvious, but it took me some time to figure what was going on, so you guys may consider adding a note on that to the documentation :-)

[jonasrauber]

Thanks Ivan, we certainly need to improve the documentation.

Would you have expected a different syntax to specify a custom session? Maybe we can make it easier to use TensorFlowModel.

[ivust]

Maybe there could be an optional argument for a user-defined session in the TensorFlowModel:

TensorFlowModel(images, logits, bounds, channel_axis=3, user_session=None)

If no session if provided, then TensorFlowModel can do what it does now, but maybe also throw a warning that a new session has been created and some variables have been initialised to their default values.

[jonasrauber]

I added a new page in the documentation with examples, in particular lot's of examples of the different ways to create a foolbox.models.TensorFlowModel: https://foolbox.readthedocs.io/en/latest/user/examples.html

@ivust What you are using right now is basically Option 4. Have a look at the other options, I think Option 1, Option 2 and Option 3 are nicer.

Your proposal,

session = tf.Session()
restorer.restore(session, '/path/to/vgg_19.ckpt')
model = foolbox.models.TensorFlowModel(images, logits, (0, 255), session=session)
print(np.argmax(model.predictions(image)))
session.close()

is basically a fifth option that's almost identical to Option 3 and therefore will not be implemented for now (I would however accept pull-requests for this, if you really want it).

[jonasrauber]

Considering this solved. @ivust let me know if I missed something.