Deprecate `test_value` machinery

[ricardoV94]

Description

This adds a lot of complexity for little user benefit (most don't know about this functionality in the first place)

[ricardoV94]

A first pass would be to just put FutureWarnings in the right places, when flags are changed or test values accessed from tags.

As a smaller scope alternative, it would be nice to have a helper that computes intermediate values for all variables in a graph so we can show them in dprint.

Something like:

def eval_intermediate_values(
  variables: Union[Sequence[Variable], FunctionGraph],
  vars_to_values: Mapping[Variable, Any],
) -> Mapping[Variable, Any] :

For instance

x = pt.scalar("x")
y = x - 1
z = pt.log(y)

eval_intermediate_values(z, {x: 0.5})
# {x: 0.5, y: -0.5, z: nan}

[ferrine]

A first pass would be to just put FutureWarnings in the right places, when flags are changed or test values accessed from tags.

As a smaller scope alternative, it would be nice to have a helper that computes intermediate values for all variables in a graph so we can show them in dprint.

Something like:

def eval_intermediate_values(
  variables: Union[Sequence[Variable], FunctionGraph],
  vars_to_values: Mapping[Variable, Any],
) -> Mapping[Variable, Any] :

For instance

x = pt.scalar("x")
y = x - 1
z = pt.log(y)

eval_intermediate_values(z, {x: 0.5})
# {x: 0.5, y: -0.5, z: nan}

Can this approach lead to out of memory in some scenarios?

[ferrine]

Moreover the eval_intermediate_values seem to be useless since for small graphs you can eval by hand and for large graphs there is no idea what is a variable corresponding to and what leads to nans

[ricardoV94]

Moreover the eval_intermediate_values seem to be useless since for small graphs you can eval by hand and for large graphs there is no idea what is a variable corresponding to and what leads to nans

The idea of that is that you can see it in dprint, which you can already with test values. That's useful because it shows which operations produced nans

[ricardoV94]

Can this approach lead to out of memory in some scenarios?

This wouldn't take up more memory than the current test value approach so I don't think it's an important concern

[ricardoV94]

The idea of that is that you can see it in dprint, which you can already with test values. That's useful because it shows which operations produced nans

Apparently I imagined that functionality. I still think it could be worth exploring but can be done in a separate issue.

[ricardoV94]

Here is the kind of thing I had in mind:

import numpy as np
import pytensor
import pytensor.tensor as pt

pytensor.config.compute_test_value = "warn"
x = pt.vector("x")
x.tag.test_value = np.array([1, -2, 3])
y = pt.exp(pt.log(pt.tanh(x * 2)) + 3).sum()

pytensor.dprint(y)
# Sum{axes=None} [id A]nan
#  └─ Exp [id B][19.36301155         nan 20.08529011]
#     └─ Add [id C][2.96336463        nan 2.99998771]
#        ├─ Log [id D][-3.66353747e-02             nan -1.22884247e-05]
#        │  └─ Tanh [id E][ 0.96402758 -0.9993293   0.99998771]
#        │     └─ Mul [id F][ 2. -4.  6.]
#        │        ├─ x [id G][ 1. -2.  3.]
#        │        └─ ExpandDims{axis=0} [id H][2]
#        │           └─ 2 [id I]
#        └─ ExpandDims{axis=0} [id J][3]
#           └─ 3 [id K]

[ricardoV94]

Here is another idea about providing more useful test_value-like machinery, that need not be so ingrained in the PyTensor codebase: https://gist.github.com/ricardoV94/e8902b4c35c26e87e189ab477f8d9288

[Dhruvanshu-Joshi]

Hi @ricardoV94 So in the following lines: https://github.com/pymc-devs/pytensor/blob/dbe0e09ae2a5f5d0119e0378259f843a95d36abc/pytensor/graph/op.py#L303-L304

will we want to add a warning whenever config.compute_test_value != "off" or in cases whenever compute_test_value is called?

Going by the first logic: https://github.com/pymc-devs/pytensor/blob/dbe0e09ae2a5f5d0119e0378259f843a95d36abc/pytensor/graph/op.py#L671-L677

we will raise a warning here only when assert action in ("ignore", "off") fails right (I am not sure we should raise a warning when assert itself fails?)

[Dhruvanshu-Joshi]

I think the warnings make sense when config.compute_test_value!="off" and when tag.test_value is accessed ( which automatically includes the get_test_value cases). Is this correct?

[ricardoV94]

Yes, that's probably a good start. Then the challenging part is making sure we don't use those anywhere internally, other than direct tests of the test_value machinery (and those we just put a with pytest.warns everytime we expect the functionality to be used.