Improved exception handling

[rafaelha]

Slight normalization issues no longer raise an error but a warning. These can occur for circuits with arbitrary rotation gates, where fp32 is used instead of an exact representation.

Parsing errors for invalid Stim circuits now raise useful exceptions.

[github-actions]

☂️ Python Coverage

current status: ✅

Overall Coverage

Lines	Covered	Coverage	Threshold	Status
2146	2073	97%	0%	🟢

New Files

No new covered files...

Modified Files

File	Coverage	Status
src/tsim/circuit.py	94%	🟢
src/tsim/core/parse.py	93%	🟢
src/tsim/sampler.py	97%	🟢
src/tsim/utils/program_text.py	95%	🟢
TOTAL	95%	🟢

updated for commit: 59daecc by action🐍

[github-actions]

PR Preview Action v1.8.1
Preview removed because the pull request was closed.
2026-04-06 17:40 UTC

[Copilot]

Pull request overview

This PR improves error reporting and robustness around parsing tsim shorthand/Stim program text, and adjusts sampler behavior to warn (instead of error) on small normalization deviations.

Changes:

• Add scientific-notation support for parametric angles in shorthand parsing and tag parsing, with new unit tests.
• Enrich Stim parse errors to surface the problematic unconverted shorthand snippet in Circuit construction/append paths.
• Change sampler normalization handling from raising to warning for small deviations, and update integration expectations; also refactor transversal encoder behavior (gate expansion removal).

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/tsim/utils/program_text.py	Adds scientific-notation parsing and introduces enriched Stim error extraction helpers.
src/tsim/circuit.py	Uses enriched parsing errors when constructing/appending circuits; replaces asserts with ValueError for invalid parametric usage.
src/tsim/core/parse.py	Extends parametric tag parsing regex to allow scientific notation.
src/tsim/sampler.py	Switches normalization failures from exception to warning (and introduces a new underflow ValueError path).
src/tsim/utils/encoder.py	Removes logical gate expansion behavior from transversal encoding logic and constructor surface.
test/unit/utils/test_program_text.py	Adds tests for scientific notation and for enriched parse-error snippets.
test/integration/test_sampler.py	Updates expectations to warning (instead of raising) on normalization deviation.

Comments suppressed due to low confidence (1)

src/tsim/core/parse.py:58

• parse_parametric_tag now accepts scientific notation via regex, but still does Fraction(param_match.group(2)). fractions.Fraction does not accept strings like "1e-2", so tags produced with scientific notation (e.g. theta=1e-6*pi) will raise instead of parsing. Convert via Decimal (e.g. Fraction(Decimal(value_str))) or via Fraction.from_float(float(value_str)).limit_denominator(...) to actually support the new accepted formats.

        # Match param=value*pi (value can be negative/decimal/scientific)
        param_match = re.match(
            r"^(\w+)=([-+]?(?:\d+\.?\d*|\.\d+)(?:[eE][-+]?\d+)?)\*pi$", param
        )
        if not param_match:
            return None
        param_name = param_match.group(1)
        value = Fraction(param_match.group(2))
        params[param_name] = value

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