Picklability

[bartvm]

As mentioned by @dmitriy-serdyuk in #1 (comment) the GzipJSONHandler and PrintHandler objects aren't picklable in Python 2 (GzipJSONHandler seems fine in Python 3).

This is of course expected behaviour because pickling objects like file handles doesn't make sense most of the time, but we might need to come up with something to make Blocks' checkpointing happy.

I don't like the idea of adding all sorts of pickling magic just to accommodate Blocks, but maybe something can be done from the Blocks side instead.

[bartvm]

Also just a note that simply doing what Fuel does (use the file_iterator from picklable-itertools) won't work here, because the file object used by e.g. PrintHandler is sys.stdout which can't be pickled using the name alone.

[bartvm]

Picklable wrapper in mila-iqia/blocks#1013