refactor(distributions): now the singleton is really a singleton, some checks have been added + test covering

Author: siwreienta

src/pysatl_core/distributions/computations/continuous.py

@@ -346,15 +346,26 @@ def _fit_ppf_to_cdf_1C(
         lower bound of the CDF domain approximation.
     q_highest : float, default 1 - 1e-12
         *(Characteristic option)* Right bracket for root search.  Defines the
-        upper bound of the CDF domain approximation.
+        upper bound of the CDF domain approximation.  Must be strictly greater
+        than *q_lowest*.
     max_iter : int, default 256
         *(Computation option)* Maximum brentq iterations per point.
 
     Returns
     -------
     FittedComputationMethod[NumericArray, NumericArray]
         Array-semantic ``cdf`` callable.
+
+    Raises
+    ------
+    ValueError
+        If ``q_highest <= q_lowest``.
     """
+    if q_highest <= q_lowest:
+        raise ValueError(
+            f"q_highest must be greater than q_lowest, got q_lowest={q_lowest!r}, "
+            f"q_highest={q_highest!r}."
+        )
     ppf_func = resolve(distribution, CharacteristicName.PPF)
 
     def _cdf(x: NumericArray, **options: Any) -> NumericArray:

src/pysatl_core/distributions/computations/registry.py

@@ -17,7 +17,7 @@
 __license__ = "SPDX-License-Identifier: MIT"
 
 from functools import lru_cache
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, Any, ClassVar, Self
 
 if TYPE_CHECKING:
     from collections.abc import Sequence
@@ -30,19 +30,50 @@ class FitterRegistry:
     """
     Registry that stores fitter descriptors and selects the best match.
 
+    This class is a singleton: every call to ``FitterRegistry()`` returns the
+    same instance.  Use ``FitterRegistry._reset()`` in tests to clear state.
+
     Examples
     --------
     >>> registry = FitterRegistry()
     >>> registry.register(some_descriptor)
     >>> desc = registry.find("cdf", ["pdf"], required_tags={"continuous", "univariate"})
     """
 
+    _instance: ClassVar[FitterRegistry | None] = None
+
+    def __new__(cls) -> Self:
+        if cls._instance is None:
+            cls._instance = super().__new__(cls)
+        return cls._instance  # type: ignore[return-value]
+
     def __init__(self) -> None:
+        if getattr(self, "_initialized", False):
+            return
         self._by_key: dict[
             tuple[GenericCharacteristicName, tuple[GenericCharacteristicName, ...]],
             list[FitterDescriptor],
         ] = {}
         self._all: list[FitterDescriptor] = []
+        self._initialized = True
+
+    def __copy__(self) -> Self:
+        """Singleton copy returns the same instance."""
+        return self
+
+    def __deepcopy__(self, memo: dict[Any, Any]) -> Self:
+        """Singleton deepcopy returns the same instance."""
+        return self
+
+    @classmethod
+    def _reset(cls) -> None:
+        """
+        Clear the singleton instance (for testing purposes only).
+
+        Resets all registered descriptors and allows the next ``FitterRegistry()``
+        call to create a fresh instance.
+        """
+        cls._instance = None
 
     def register(self, descriptor: FitterDescriptor) -> None:
         """
@@ -153,8 +184,9 @@ def fitter_registry() -> FitterRegistry:
     -----
     - Descriptors are **not** created at import time; they are built here on
       first access, keeping module-level side-effects to a minimum.
-    - Users who need a custom registry should instantiate ``FitterRegistry()``
-      directly and populate it themselves.
+    - ``FitterRegistry`` is a singleton; ``FitterRegistry() is fitter_registry()``
+      is always ``True`` after the first call.
+    - To reset the singleton (e.g. in tests), call ``reset_fitter_registry()``.
     """
     from pysatl_core.distributions.computations.continuous import (
         _build_continuous_descriptors,
@@ -172,6 +204,7 @@ def fitter_registry() -> FitterRegistry:
 def reset_fitter_registry() -> None:
     """Reset the cached fitter registry (useful in tests)."""
     fitter_registry.cache_clear()
+    FitterRegistry._reset()
 
 
 __all__ = [

src/pysatl_core/distributions/registry/configuration.py

@@ -26,7 +26,7 @@
 from functools import lru_cache
 from typing import TYPE_CHECKING
 
-from pysatl_core.distributions.computations.registry import FitterRegistry, fitter_registry
+from pysatl_core.distributions.computations.registry import fitter_registry
 from pysatl_core.distributions.registry.constraint import (
     GraphPrimitiveConstraint,
     NonNullConstraint,
@@ -48,7 +48,6 @@
 
 def _add_edges(
     reg: CharacteristicRegistry,
-    fitter_reg: FitterRegistry,
     pairs: Iterable[tuple[GenericCharacteristicName, GenericCharacteristicName]],
     *,
     tags: frozenset[str],
@@ -62,8 +61,6 @@ def _add_edges(
     ----------
     reg : CharacteristicRegistry
         Target characteristic graph.
-    fitter_reg : FitterRegistry
-        Index of fitter descriptors to query.
     pairs : Iterable[tuple[str, str]]
         ``(source, target)`` pairs to register.
     tags : frozenset[str]
@@ -76,6 +73,7 @@ def _add_edges(
     RuntimeError
         If no descriptor matches one of the requested ``(source, target, tags)``.
     """
+    fitter_reg = fitter_registry()
     for src, tgt in pairs:
         descriptor = fitter_reg.find(tgt, [src], required_tags=tags)
         if descriptor is None:
@@ -92,8 +90,6 @@ def _add_edges(
 
 def _configure(reg: CharacteristicRegistry) -> None:
     """Default PySATL configuration for characteristic registry."""
-    fitter_reg = fitter_registry()
-
     dim1_constraint = NumericConstraint(allowed=frozenset({1}))
     kind_continuous = SetConstraint(allowed=frozenset({Kind.CONTINUOUS}))
     kind_discrete = SetConstraint(allowed=frozenset({Kind.DISCRETE}))
@@ -144,7 +140,6 @@ def _configure(reg: CharacteristicRegistry) -> None:
 
     _add_edges(
         reg,
-        fitter_reg,
         pairs=(
             (CharacteristicName.PDF, CharacteristicName.CDF),
             (CharacteristicName.CDF, CharacteristicName.PDF),
@@ -157,7 +152,6 @@ def _configure(reg: CharacteristicRegistry) -> None:
 
     _add_edges(
         reg,
-        fitter_reg,
         pairs=(
             (CharacteristicName.PMF, CharacteristicName.CDF),
             (CharacteristicName.CDF, CharacteristicName.PMF),

src/pysatl_core/distributions/strategies.py

@@ -727,9 +727,9 @@ def query_method(
 
         self._push_guard(distr, state)
         self._char_options_stack.append(dict(effective_char_options))
+        injected_keys: list[tuple[int, GenericCharacteristicName]] = []
         try:
             last_fitted: FittedComputationMethod[Any, Any] | None = None
-            injected_keys: list[tuple[int, GenericCharacteristicName]] = []
             for step_idx, edge in enumerate(cached_plan.edges):
                 method = edge.method
 
@@ -783,14 +783,14 @@ def query_method(
                 )
                 injected_keys.append(intermediate_key)
 
-            # Remove the temporary loop plans injected for intermediate targets.
-            for key in injected_keys:
-                self._path_cache.pop(key, None)
-
             if last_fitted is None:
                 raise RuntimeError(f"Empty path when resolving '{state}'.")
             return last_fitted
         finally:
+            # Remove the temporary loop plans injected for intermediate targets.
+            # Placed in finally to ensure cleanup even if fitting raises.
+            for key in injected_keys:
+                self._path_cache.pop(key, None)
             self._char_options_stack.pop()
             self._pop_guard(distr, state)
 

tests/unit/distributions/computations/test_registry.py

@@ -10,8 +10,10 @@
 
 from typing import Any
 
+import pytest
+
 from pysatl_core.distributions.computations.descriptors import FitterDescriptor
-from pysatl_core.distributions.computations.registry import FitterRegistry
+from pysatl_core.distributions.computations.registry import FitterRegistry, reset_fitter_registry
 from pysatl_core.types import CharacteristicName
 
 
@@ -37,6 +39,11 @@ def _make_desc(
 class TestFitterRegistry:
     """Tests for the FitterRegistry class."""
 
+    @pytest.fixture(autouse=True)
+    def reset_registry(self) -> None:
+        """Reset the FitterRegistry singleton before each test."""
+        reset_fitter_registry()
+
     def test_register_and_find(self) -> None:
         reg = FitterRegistry()
         desc = _make_desc("pdf_to_cdf")
@@ -140,6 +147,16 @@ def test_contains(self) -> None:
         assert "pdf_to_cdf" in reg
         assert "nonexistent" not in reg
 
+    def test_singleton_returns_same_instance(self) -> None:
+        reg1 = FitterRegistry()
+        reg2 = FitterRegistry()
+        assert reg1 is reg2
+
+    def test_fitter_registry_function_returns_same_instance(self) -> None:
+        from pysatl_core.distributions.computations.registry import fitter_registry
+
+        assert FitterRegistry() is fitter_registry()
+
     def test_different_source_target_pairs_are_independent(self) -> None:
         reg = FitterRegistry()
         pdf_cdf = _make_desc(