Add lalib.config for library-wide settings

Also, refactor `lalib.elements.galois`
(incl. tests) to use the new settings

src/lalib/config.py

@@ -0,0 +1,5 @@
+"""Library-wide default settings."""
+
+NDIGITS = 12
+
+THRESHOLD = 1 / (10**NDIGITS)

src/lalib/elements/galois.py

@@ -43,14 +43,14 @@ except ImportError:  # pragma: no cover to support Python 3.9 & 3.10
     from typing_extensions import Self
 
 
-THRESHOLD = 1e-12
+from lalib import config
 
 
 def _to_gf2(
     value: complex,  # `mypy` reads `complex | float | int`
     *,
     strict: bool = True,
-    threshold: float = THRESHOLD,
+    threshold: float = config.THRESHOLD,
 ) -> int:
     """Cast a number as a possible Galois field value: `1` or `0`.
 
@@ -132,7 +132,7 @@ class GF2Element(metaclass=GF2Meta):
         value: object = None,
         *,
         strict: bool = True,
-        threshold: float = THRESHOLD,
+        threshold: float = config.THRESHOLD,
     ) -> Self:
         """See docstring for `.__init__()`."""
         if isinstance(value, cls):
@@ -162,7 +162,7 @@ class GF2Element(metaclass=GF2Meta):
         value: object = None,
         *,
         strict: bool = True,
-        threshold: float = THRESHOLD,
+        threshold: float = config.THRESHOLD,
     ) -> None:
         """Obtain one of two objects: `one` or `zero`.
 
@@ -242,7 +242,7 @@ class GF2Element(metaclass=GF2Meta):
         """Round `self` up to the next `int`: `math.ceil(self)`."""
         return int(self)
 
-    def __round__(self, ndigits: Optional[int] = 0) -> int:
+    def __round__(self, _ndigits: int = config.NDIGITS) -> int:
         """Round `self` to the next `int`: `round(self)`."""
         return int(self)
 
@@ -556,3 +556,5 @@ gf2 = GF2Element
 del GF2Meta
 del GF2One
 del GF2Zero
+
+del config

tests/elements/test_galois.py

@@ -11,6 +11,7 @@ import sys
 
 import pytest
 
+from lalib import config
 from lalib.elements import galois
 
 
@@ -26,17 +27,15 @@ GF2Element, GF2One, GF2Zero = (  # not part of the official API
     type(galois.zero),  # are deleted in `lalib.elements.galois`
 )
 
-_THRESHOLD = galois.THRESHOLD
-
 del galois
 
 
 CROSS_REFERENCE = not os.environ.get("NO_CROSS_REFERENCE")
 
 
-default_threshold = _THRESHOLD
-within_threshold = _THRESHOLD / 10
-not_within_threshold = _THRESHOLD * 10
+default_threshold = config.THRESHOLD
+within_threshold = config.THRESHOLD / 10
+not_within_threshold = config.THRESHOLD * 10
 
 strict_one_like_values = (
     1,