Abstract syntax tree parser for ConfigSpace by thijssnelleman · Pull Request #413 · automl/ConfigSpace

thijssnelleman · 2025-09-30T06:38:55Z

Adding in logic for parsing expressions into ConfigSpace Conditions/Forbiddens. This is aimed to take general logic expressions (strings) and uses the AST library to convert it into a ConfigSpace expression.

The reason of this being necessary is as a build up towards enabling parsing a ConfigSpace from other notation files, such as PCS files from SMAC2, IRACE etc.

…hon >= 3.9

thijssnelleman · 2025-12-19T13:03:13Z

TODO: Add more docs into the methods, s.t. we have examples for the documentation site

…tract-syntax-tree-parser

thijssnelleman · 2026-01-05T09:19:43Z

@mfeurer

Added new docs example for usage, cleaned up code and other comments. I think its ready for a review now.

thijssnelleman · 2026-01-20T14:22:13Z

@mfeurer Reminder for this PR

Copilot

Pull request overview

Adds an AST-based parser that converts string logic expressions into ConfigSpace Condition or ForbiddenClause objects, to support importing ConfigSpaces from external notations (e.g., PCS/SMAC/IRACE).

Changes:

Introduces expression_to_configspace() (and a recursive AST conversion helper) to map comparisons and boolean logic into ConfigSpace Conditions/Forbiddens.
Adds unit tests covering basic parsing cases (value comparisons, HP relations, conjunctions/disjunctions, in).
Extends imports to include additional Forbidden clause/conjunction types used in the new tests.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 7 comments.

File	Description
`src/ConfigSpace/util.py`	Adds AST parsing and recursive conversion into ConfigSpace Condition/Forbidden objects.
`test/test_util.py`	Adds tests for `expression_to_configspace()` covering simple/complex expressions and error cases.

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mfeurer · 2026-04-01T13:48:01Z

test/test_util.py

+    wrong_expression = "a >!> b"
+    with pytest.raises(ValueError):
+        expression_to_configspace(wrong_expression, cs)
+
+    wrong_hp_name_expresion = "q <= 5"
+    with pytest.raises(ValueError):
+        cs_expression = expression_to_configspace(wrong_hp_name_expresion, cs)
+
+    wrong_hp_value_expression = "a > 11"
+    with pytest.raises(ValueError):
+        cs_expression = expression_to_configspace(wrong_hp_value_expression, cs)
+
+    wrong_hp_value_expression = "a == dog"
+    with pytest.raises(ValueError):
+        cs_expression = expression_to_configspace(wrong_hp_value_expression, cs)


Did you add the check for "a != b"?

mfeurer · 2026-04-01T13:48:55Z

src/ConfigSpace/util.py

+    expression = re.sub(r" != ", " = ", expression)
+    expression = re.sub(r" (?<![<>!=])=(?<![=]) ", " == ", expression)


It seems like you have not incorporated this, was this wrong?

src/ConfigSpace/util.py

test/test_util.py

src/ConfigSpace/util.py

…tract-syntax-tree-parser

Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

karibbov · 2026-03-17T13:04:33Z

Hi, I'm finally able to wrap my head around what expression_to_configspace does. Thanks for your patience 😅

TL;DR: expression_to_configspace works as expected and parses ast expressions to be either Forbidden expressions or Condiditional statements depending on if the target_hyperparameters argument is passed into it. It's compexity is necessary, but I think we can wrap it into two different functions to keep the api clean and easy to understand.

Summary

expression_to_configspace does two different things:

When the target_hyperparameter argument is not provided, it'll parse the expression as forbidden. This means the (ast) expression will never resolve to true across the samples from the configspace.
When the target_hyperparameter argument is provided, it'll parse the expression as a conditional expression, where the target_hyperparameter will be conditional hyperparameters. In this case the expression (if expression -> conditional_hyperparameter) will always be true. The final result is essentially the inverse of the first case, which makes the function api confusing without diving deep into the implementation details of ConfigSpace. Furthermore, some expressions, such as HP relations and non-strict inequalities are not supported for conditional HPs but are for Forbiddens.

Suggestions

We can instead offer 2 wrapper functions: forbidden_expression_from_ast and conditional_expression_from_ast, where the former does not expose the target_hyperparameter argument while the second one requires it.
This would also make the testing cleaner, as we can test both functionalities separately and add complex expression tests for conditional HPs as well.
I would also suggest considering to refactor expression_to_configspace -> expression_from_ast (to further prevent confusion if this function would actually add the expression to the configspace or not) and target_hyperparameter -> conditional_hyperparameter (more explicit).

thijssnelleman · 2026-03-17T13:42:13Z

Hi, I'm finally able to wrap my head around what expression_to_configspace does. Thanks for your patience 😅

TL;DR: expression_to_configspace works as expected and parses ast expressions to be either Forbidden expressions or Condiditional statements depending on if the target_hyperparameters argument is passed into it. It's compexity is necessary, but I think we can wrap it into two different functions to keep the api clean and easy to understand.

Summary

expression_to_configspace does two different things:

When the target_hyperparameter argument is not provided, it'll parse the expression as forbidden. This means the (ast) expression will never resolve to true across the samples from the configspace.

When the target_hyperparameter argument is provided, it'll parse the expression as a conditional expression, where the target_hyperparameter will be conditional hyperparameters. In this case the expression (if expression -> conditional_hyperparameter) will always be true. The final result is essentially the inverse of the first case, which makes the function api confusing without diving deep into the implementation details of ConfigSpace. Furthermore, some expressions, such as HP relations and non-strict inequalities are not supported for conditional HPs

Suggestions

We can instead offer 2 wrapper functions: forbidden_expression_from_ast and conditional_expression_from_ast, where the former does not expose the target_hyperparameter argument while the second one requires it.

This would also make the testing cleaner, as we can test both functionalities separately and add complex expression tests for conditional HPs as well.

I would also suggest considering to refactor expression_to_configspace -> expression_from_ast (to further prevent confusion if this function would actually add the expression to the configspace or not) and target_hyperparameter -> conditional_hyperparameter (more explicit).

Agreed with point three, renaming is much more clear to the user for the parameter (Although @mfeurer may argue that it should be named child_hyperparameter to be consistent with other code?). I have updated the code accordingly.
However I disagree with the function rename as we are not converting from ast, but from strings. Perhaps a slightly different name may be more clear? expression_from_string?
I also do not think we should offer two entry points wrapping the underlying function, unless there is a clear user demand for it. The current workflow is documented so it's relatively easy for users to understand it. Although it would be a very clear separation indeed.

karibbov · 2026-03-17T14:01:17Z

Fair points! I don't have strong opinions about the user base or the naming conventions yet 😄. We can merge if @mfeurer also doesn't have strong opinions against it.

mfeurer

Here we go. I think the code is fine, but I have not gone through the whole logic of the parsing and rather assume that the tests are correct.

I don't think that the function name is great yet, maybe something like parse_expression_from_string(). Besides that, I don't have strong opinions on having one or two functions, and think we can go with a single function for now.

docs/reference/util.md

test/test_util.py

mfeurer · 2026-04-01T13:48:01Z

test/test_util.py

+    wrong_expression = "a >!> b"
+    with pytest.raises(ValueError):
+        expression_to_configspace(wrong_expression, cs)
+
+    wrong_hp_name_expresion = "q <= 5"
+    with pytest.raises(ValueError):
+        cs_expression = expression_to_configspace(wrong_hp_name_expresion, cs)
+
+    wrong_hp_value_expression = "a > 11"
+    with pytest.raises(ValueError):
+        cs_expression = expression_to_configspace(wrong_hp_value_expression, cs)
+
+    wrong_hp_value_expression = "a == dog"
+    with pytest.raises(ValueError):
+        cs_expression = expression_to_configspace(wrong_hp_value_expression, cs)


Did you add the check for "a != b"?

mfeurer · 2026-04-01T13:48:55Z

src/ConfigSpace/util.py

+    expression = re.sub(r" != ", " = ", expression)
+    expression = re.sub(r" (?<![<>!=])=(?<![=]) ", " == ", expression)


It seems like you have not incorporated this, was this wrong?

src/ConfigSpace/util.py

test/test_util.py

src/ConfigSpace/util.py

thijssnelleman added 2 commits September 22, 2025 17:56

First version

469d059

Expanding tests

7642320

thijssnelleman requested a review from mfeurer September 30, 2025 06:39

thijssnelleman added 2 commits September 30, 2025 09:14

Simplifying print statement as ast.unparse is only available from Pyt…

753fa8d

…hon >= 3.9

Bugfixes

92d450d

thijssnelleman added 5 commits December 19, 2025 14:34

Updating documentation

de35995

Merge branch 'main' of https://github.com/automl/ConfigSpace into abs…

c209f0f

…tract-syntax-tree-parser

Cleaning up code, expanding docs

be3db2d

bugfix

4b344dc

docs typo

83119dd

mfeurer requested a review from Copilot March 16, 2026 12:38

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thijssnelleman and others added 11 commits March 16, 2026 14:15

Adding docs, minor fixes

76d6617

Merge branch 'main' of https://github.com/automl/ConfigSpace into abs…

f165c9e

…tract-syntax-tree-parser

Fixing example

03a9790

Remove mistake file

2f1c563

docfix

995f02e

Potential fix for pull request finding

96f6dca

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Potential fix for pull request finding

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Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>

Updating copilot fix, adding tests

bb199bb

Bugfixes

1f1a609

docfix

3d1f4ba

reference fix

2192f7f

Parameter rename

fc11a3b

karibbov requested a review from mfeurer March 17, 2026 14:06

karibbov approved these changes Mar 17, 2026

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mfeurer reviewed Apr 1, 2026

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thijssnelleman added 9 commits April 1, 2026 17:35

Rename function

d2ebe05

Separating the examples as two subsections

b839258

Fixing pytest message check

ca5d3b7

docstring fix

88bbcdf

seperating test in two parts

af3d63f

Adding test

6f16277

Clarification for possible ambiguity, adding tests

2f769e7

Updating method to be more strict on HP names

fa9ea17

Docs clarification

b5eef6f

mfeurer reviewed Apr 2, 2026

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removing commented out code

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mfeurer approved these changes Apr 2, 2026

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mfeurer merged commit 3bde479 into main Apr 2, 2026
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mfeurer deleted the abstract-syntax-tree-parser branch April 2, 2026 13:00

		expression = re.sub(r" != ", " = ", expression)
		expression = re.sub(r" (?<![<>!=])=(?<![=]) ", " == ", expression)

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thijssnelleman commented Sep 30, 2025

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thijssnelleman commented Mar 17, 2026

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karibbov commented Mar 17, 2026 •

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