Consistent interface for algorithms & single training script

[AdamGleave]

Currently we don't have any CLI script for behavioral cloning or the density baseline. I envisage this codebase as being particularly useful in being able to rapidly benchmark against a wide variety of algorithms. For this to be possible, we need to have (as far as is possible) a consistent interface between different imitation learning algorithms, similarly to how Stable Baselines has a similar interface for all RL algorithms implemented. Ideally we'd then also have imitation.scripts.train work for all of them, although there'll clearly need to be som algorithm-specific configs.

[shwang]

We now have a SB3-like .train(total_timesteps) interface for GAIL, AIRL, DAgger, and BC. Also we have Sacred scripts for each of these algorithms, though they are not unified into a single train.

[AdamGleave]

We've made a lot of progress since this issue was first opened but there's still room for improvement so I'm leaving this open for now.

[ernestum]

I think this issue is required before we can address #587 and start a new take on #602.
I reviewed the scripts and this are some points we should address:

This is the current relationship between scripts and algorithms

Algo	Script	comments
DAgger, BC	train_imitation	BC is a "hidden feature" by setting use_dagger=False
MCE IRL	-	do we need a script for this?
AIRL, GAIL	train_adversarial	They being thrown together into one script results in lots of weird constructs such as an algorithm_specific configuration that are merged with the config using dubious hacks and configuration being modified during runtime.
PreferenceComparisons	train_preference_comparisons	-

There is a reward ingredient, that should probably be called reward_net. It takes care of edge cases for AIRL which I think is a bad idea. It also has some named configs that only enable/disable individual configurations. I think this is something that should be handled by the config_hook.

There is a train ingredient which should be split up into a policy and an evaluation ingredient. Ingredients are objects, not verbs.

We should probably have an ingredient for each algorithm. This makes constructing more complex experiments (such as warm-starting) easier.
I also would vote for one train_<algo> script per algorithm to follow unix philosophy that each tool should only do one job.

[AdamGleave]

We should probably have an ingredient for each algorithm. This makes constructing more complex experiments (such as warm-starting) easier.

Note sacred.Experiment is-a sacred.Ingredient (parent class), so I think we already have this more or less? EDIT: After seeing #663 I do think there's a case for making BC an ingredient if we want to use it to warm-start a variety of other algorithms, and because it already has a compositional relationship with DAgger. BC might be a bit of a special case in that regard though.

I also would vote for one train_ script per algorithm to follow unix philosophy that each tool should only do one job.

I feel torn here. It's nice to be able to do benchmarks with a variety of algorithms using a consistent interface. Having one script with different subcommands seems more natural here. You could split it up into different scripts, but it seems like a bit of a nightmare to maintain a consistent interface across many files, although perhaps doable if we can factor out most things into ingredients?

However, the algorithms do have different enough fundamental properties we can't literally have the same interface for all. Current approach was a compromise grouping similar algorithms together: e.g. AIRL/GAIL are almost identical except for the parametric form of reward network. But I agree the way they (and BC/DAgger) are currently merged is pretty ad-hoc.

Before we do a complete rewrite of the scripts I do think it's worth reflecting whether we want to keep building on top of Sacred. I do like it but the project is sadly basically abandonware at this point.

[ernestum]

Good point, that each Experiment is actually an Ingredient. I will double-check where it makes sense to turn algorithms to ingredients. It would be pointless to have e.g. a DAggerExperiment who only as a single DAggerIngredient.

IMO the consistent interface should result from a consistent design of the ingredients and their configuration. The scripts just pull together the ingredients to form experiments. They allow to run an experiment with the given ingredients but also to explore what configuration values are needed for it. When I run python -m imitation.scripts.<some_script> print_config I expect it to only show me the configuration specific to what <some_script> does. E.g. right now we use the train_imitation to train BC as well as DAgger. If I am only interested in training BC, then I don't want to be bothered with the configuration values for DAgger in the print_config output.

Throwing together AIRL and GAIL eventually resulted in some weird design choices (see comments in above table). It is tempting to fuse them since they are so similar but I feel like the decision to generalize here (which is a good idea on its own) required so many hacks that the gained elegance/reduction of redundancy was outweighed.

I totally agree that we should review the usage of Sacred before we put too much time into refactoring the scripts.
Why do you believe that Sacred is abandoned? When I look just at their releases page it does not seem too bad.
Alternatives to consider are Guild AI and MLFlow. After a quick glance Guild AI looks more promising but we should investigate this more in-depth.

[AdamGleave]

E.g. right now we use the train_imitation to train BC as well as DAgger. If I am only interested in training BC, then I don't want to be bothered with the configuration values for DAgger in the print_config output.

That's a good point, I think I'm convinced it's worth splitting up scripts, so long as we can avoid substantial code duplication by splitting things into ingredients.

Throwing together AIRL and GAIL eventually resulted in some weird design choices (see comments in above table). It is tempting to fuse them since they are so similar but I feel like the decision to generalize here (which is a good idea on its own) required so many hacks that the gained elegance/reduction of redundancy was outweighed.

I agree there's a lot of hacks. I still feel a bit uncertain about this, probably easier to discuss with a concrete idea of how to split them up and what can be shared via ingredients etc. It would be nice to have an easy way to use shared configs between AIRL/GAIL as the right hyperparameters are often quite similar, although this use case is less common now we're using automatically tuned hyperparameters (the configs saved in benchmarks/).

I totally agree that we should review the usage of Sacred before we put too much time into refactoring the scripts. Why do you believe that Sacred is abandoned? When I look just at their releases page it does not seem too bad. Alternatives to consider are Guild AI and MLFlow. After a quick glance Guild AI looks more promising but we should investigate this more in-depth.

Abandoned was too strong a word. The original maintainers of Sacred stepped back from the project and did not handover cleanly. Currently @thequilo has been doing a heroic job reviewing and fixing outstanding issues, and things are improving now that he's got access to make PyPI releases. However, the situation is a bit precarious: if @thequilo leaves there's no ones, and he still doesn't have full permissions on the project. IDSIA/sacred#871 (comment) and IDSIA/sacred#879 have some relevant discussion.

Thanks for looking into alternatives. From a quick skim of Guild AI's docs agree it seems promising, though some design decisions I feel hesitant about (e.g. treating global constants as flags by default...)

[thequilo]

@AdamGleave is not wrong, there is a risk of sacred becoming unmaintained when I step out. As I am currently a Ph.D. student, and it's completely unclear what will happen after I finished my Ph.D., this might happen in the not-so-far future. But, since my lab is heavily using sacred for all experiment tracking, I'm sure we'll find someone from my lab to continue to maintain sacred, given that Qwlouse gives us access.

[AdamGleave]

Thanks for clarifying @thequilo -- good to know someone else in your lab is likely to pick it up. And good luck wrapping up your PhD!

[ernestum]

I had a deeper look at Guild AI, ML Flow and neptune.ai. They all are mostly geared to logging, analysis and reproducibility. In comparison to sacred they lack the (hierarchical) configuration management system with experiments and (reusable) ingredients.

I think we have two options here:
(would be interested in your opinion @AdamGleave ? I would lean towards option 1)

1. Stick with sacred

... and hope that it stays maintained. Maybe put some of our time into maintaining it if necessary, maybe push the rl-baselines-zoo to also use sacred.

Pro

• avoids lots of code duplication
• easy to add new parameters ad-hoc (no need to change config files for that)

Con

• we depend on sacred and it is unclear for how long it will be maintained
• the nested nature of experiments/ingredients invites for (often unnecessary) complexity in the experiment scripts which might sometimes outweigh the benefits of reduced code duplication

2. Use any of the other frameworks

... (probably Guild AI) and use their configuration system (or something else like argparse/click)

Pro

• We don't depend on sacred (if using Guild AI we even minimize dependency to one particular framework)
• Other tools support things like HP tuning/grid runs out of the box (no need to maintain our own parallel.py script)

Con

• We need to rewrite all our scripts
• Configuration of experiments will become harder (we need to do everything with argparse/click/global variables and there is no support for nested config scopes)

[AdamGleave]

I'll try to look at this next week. @qxcv any thoughts on above, I think you've used Sacred a fair bit?