add substitute handler

[thisiscam]

Attempt at #3124, largely mimics the lift handler

[fritzo]

Looks great and I especially like the name checking for usability!

1. Could you explain the need for the _data_cache? Would this PR break if that were missing, or is it merely for speed?
2. Could you add some unit tests in tests/poutine/test_poutines.py, perhaps forking ConditionHandlerTests?
3. Could you add an entry in docs/source/pyro.poutine.rst (inserting in alphabetical order please 😉)
4. Looks like you'll need to run make format to fix coding style (see CONTRIBUTING.md), that's why the lint stage is failing. You can test this locally via make lint.

[thisiscam]

Hi @fritzo,

My guess is: It's probably ok to drop _data_cache, assuming nothing other than concrete values are passed into the substitution. E.g. we never substitute a distribution into a variable. Otherwise, we need to make sure that if there are multiple param calls, they are substituted to point to the same object.

TBH, I have not looked into Pyro's code too much, and was largely mimicing the lift handler.

For the test case, I'm not sure how ConditionHandlerTests is relevant. Could you explain? It might be easier to add a simple standalone test case, though.

[thisiscam]

@fritzo I added some tests, but I don't know how to run the test locally... Sorry

make test

produces:

/pyro/poutine/handlers.py:docstring of pyro.poutine.handlers._make_handler.<locals>.handler:9:Unexpected indentation.

[fritzo]

I'm not sure why your local make test failed, but it might be failing linting rather than hitting the real test. To run your particular tests you could try locally pytest tests/poutine/test_poutines.py

[fritzo]

Hi @thisiscam, sorry this seems to have fallen off the radar and CI for some reason didn't trigger. Could you try merging in the dev branch and re-pushing?

[thisiscam]

@fritzo Hi, sorry about the delay. I just merged dev and pushed to my branch.
Just posting here in case GitHub didn't send a notification.

[fritzo]

Looks great, thanks for working through the CI issues.