Why is snapshot not exposed through the Python interface?

[gustavla]

I have written a Python script to manage my training and I'm adding a signal interrupt handler that upon receiving SIGTERM will finish its current iteration and then snapshot and safely quit.

However, I noticed that Solver::Snapshot is protected and thus not exposed to Python. I don't understand why this is the case, since my use case seems perfectly reasonable. Changing this locally and adding snapshot to python/_caffe.cpp has worked out well for me so far.

A way around it might be to somehow change the snapshot parameter through Python and that way force a snapshot to be made at the next iteration. I don't even know if this is possible, but even it is it's quite an ugly hack compared to just calling snapshot(). It would also delay the snapshot by one iteration.

[seanbell]

See Fast R-CNN (https://github.com/rbgirshick/fast-rcnn/blob/master/lib/fast_rcnn/train.py#L48) as an example of performing a snapshot in Python. This example has extra re-scaling of weights, but essentially you just call net.save().

[gustavla]

Calling save only produces a .caffemodel file with the weights. To correctly resume SGD with momentum, I also need the latest gradients in a .solverstate file.

[ronghanghu]

Personally I think it is better to expose Snapshot function to pycaffe. I can write a PR for that when less busy.

[gustavla]

I agree. I can also arrange a PR, since I have already made these changes locally.

[longjon]

Closing as addressed by #3082.