From 8e091d66de8e767f3d9d309f91c95d22e7bc7e5f Mon Sep 17 00:00:00 2001
From: Andrew <andrewgsavage@gmail.com>
Date: Fri, 12 Apr 2024 18:01:11 +0100
Subject: [PATCH 01/11] nonreducing

---
 pint/facets/plain/quantity.py |  2 ++
 pint/facets/plain/registry.py |  5 ++++-
 pint/util.py                  | 24 +++++++++++++++++++++++-
 3 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/pint/facets/plain/quantity.py b/pint/facets/plain/quantity.py
index 2727a7da3..72990c5d0 100644
--- a/pint/facets/plain/quantity.py
+++ b/pint/facets/plain/quantity.py
@@ -206,6 +206,8 @@ def __new__(cls, value, units=None):
         if units is None:
             units = inst.UnitsContainer()
         else:
+            if isinstance(units, list):
+                units = inst._REGISTRY.NonReducingUnitContainer(units)
             if isinstance(units, (UnitsContainer, UnitDefinition)):
                 units = units
             elif isinstance(units, str):
diff --git a/pint/facets/plain/registry.py b/pint/facets/plain/registry.py
index 277a6f7a2..e91c4d433 100644
--- a/pint/facets/plain/registry.py
+++ b/pint/facets/plain/registry.py
@@ -72,7 +72,7 @@
     string_preprocessor,
     to_units_container,
 )
-from ...util import UnitsContainer as UnitsContainer
+from ...util import UnitsContainer, NonReducingUnitContainer
 from .definitions import (
     AliasDefinition,
     CommentDefinition,
@@ -1401,6 +1401,9 @@ def UnitsContainer(self, *args: Any, **kwargs: Any) -> UnitsContainer:
 
     __call__ = parse_expression
 
+    def NonReducingUnitContainer(self, units) -> UnitsContainer:
+        return NonReducingUnitContainer(units)
+
 
 class PlainRegistry(GenericPlainRegistry[PlainQuantity[Any], PlainUnit]):
     Quantity: TypeAlias = PlainQuantity[Any]
diff --git a/pint/util.py b/pint/util.py
index 0c40c5187..48ed935a0 100644
--- a/pint/util.py
+++ b/pint/util.py
@@ -671,6 +671,26 @@ def __rtruediv__(self, other: Any):
         return self**-1
 
 
+class NonReducingUnitContainer(UnitsContainer):
+    """ The NonReducingUnitContainer stores UnitsContainers without simplifying common units.
+    This is useful when it is desired to show a unit in the numerator and denominator, eg mm/mm.
+    """
+    def __init__(
+        self, units: list[UnitsContainer] | list[tuple[QuantityOrUnitLike, Scalar]]
+    ) -> None:
+        if all(isinstance(u, tuple) for u in units):
+            units = [u[0]._units ** u[1] for u in units]
+
+        self.non_reduced_units = units
+
+        self.reduced_units = UnitsContainer()
+        for unit in units:
+            self.reduced_units *= unit
+        
+        self._d = self.reduced_units._d
+        self._hash = self.reduced_units._hash
+
+
 class ParserHelper(UnitsContainer):
     """The ParserHelper stores in place the product of variables and
     their respective exponent and implements the corresponding operations.
@@ -766,13 +786,15 @@ def from_string(cls, input_string: str, non_int_type: type = float) -> ParserHel
             reps = False
 
         gen = pint_eval.tokenizer(input_string)
+        print(build_eval_tree(gen))
         ret = build_eval_tree(gen).evaluate(
             partial(cls.eval_token, non_int_type=non_int_type)
         )
+        print(ret)
 
         if isinstance(ret, Number):
             return cls(ret, non_int_type=non_int_type)
-
+    
         if reps:
             ret = cls(
                 ret.scale,

From e8e257cec064031aa881ffb8a9b9724ce0991062 Mon Sep 17 00:00:00 2001
From: Andrew <andrewgsavage@gmail.com>
Date: Fri, 12 Apr 2024 18:14:42 +0100
Subject: [PATCH 02/11] nonreducing

---
 pint/util.py | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/pint/util.py b/pint/util.py
index 48ed935a0..91afaf644 100644
--- a/pint/util.py
+++ b/pint/util.py
@@ -786,15 +786,13 @@ def from_string(cls, input_string: str, non_int_type: type = float) -> ParserHel
             reps = False
 
         gen = pint_eval.tokenizer(input_string)
-        print(build_eval_tree(gen))
         ret = build_eval_tree(gen).evaluate(
             partial(cls.eval_token, non_int_type=non_int_type)
         )
-        print(ret)
 
         if isinstance(ret, Number):
             return cls(ret, non_int_type=non_int_type)
-    
+
         if reps:
             ret = cls(
                 ret.scale,

From 11b3ee82ba34815157fa5b0da7b0260b9d07e718 Mon Sep 17 00:00:00 2001
From: andrewgsavage <andrewgsavage@gmail.com>
Date: Wed, 22 May 2024 08:06:36 +0200
Subject: [PATCH 03/11] lint

---
 pint/facets/plain/registry.py | 3 ++-
 pint/util.py                  | 5 +++--
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/pint/facets/plain/registry.py b/pint/facets/plain/registry.py
index ab440a2a5..6e9a43bc6 100644
--- a/pint/facets/plain/registry.py
+++ b/pint/facets/plain/registry.py
@@ -63,7 +63,9 @@
 from ...errors import DimensionalityError, RedefinitionError, UndefinedUnitError
 from ...pint_eval import build_eval_tree
 from ...util import (
+    NonReducingUnitContainer,
     ParserHelper,
+    UnitsContainer,
     _is_dim,
     create_class_with_registry,
     getattr_maybe_raise,
@@ -72,7 +74,6 @@
     string_preprocessor,
     to_units_container,
 )
-from ...util import UnitsContainer, NonReducingUnitContainer
 from .definitions import (
     AliasDefinition,
     CommentDefinition,
diff --git a/pint/util.py b/pint/util.py
index ceead1463..f8e851451 100644
--- a/pint/util.py
+++ b/pint/util.py
@@ -677,9 +677,10 @@ def _normalize_nonfloat_value(self, value: Scalar) -> Scalar:
 
 
 class NonReducingUnitContainer(UnitsContainer):
-    """ The NonReducingUnitContainer stores UnitsContainers without simplifying common units.
+    """The NonReducingUnitContainer stores UnitsContainers without simplifying common units.
     This is useful when it is desired to show a unit in the numerator and denominator, eg mm/mm.
     """
+
     def __init__(
         self, units: list[UnitsContainer] | list[tuple[QuantityOrUnitLike, Scalar]]
     ) -> None:
@@ -691,7 +692,7 @@ def __init__(
         self.reduced_units = UnitsContainer()
         for unit in units:
             self.reduced_units *= unit
-        
+
         self._d = self.reduced_units._d
         self._hash = self.reduced_units._hash
 

From 4b931fa30173f5772cee63663a706bc1473f4b01 Mon Sep 17 00:00:00 2001
From: andrewgsavage <andrewgsavage@gmail.com>
Date: Fri, 24 May 2024 21:16:34 +0200
Subject: [PATCH 04/11] attempt

---
 .../formatter/_compound_unit_helpers.py       |  4 ++-
 pint/delegates/formatter/full.py              |  9 +++++-
 pint/delegates/formatter/html.py              |  2 ++
 pint/facets/plain/registry.py                 |  6 ++--
 pint/testsuite/test_unit.py                   | 13 ++++++++
 pint/util.py                                  | 32 +++++++++++++++----
 6 files changed, 55 insertions(+), 11 deletions(-)

diff --git a/pint/delegates/formatter/_compound_unit_helpers.py b/pint/delegates/formatter/_compound_unit_helpers.py
index 89bda87a2..34ffe146b 100644
--- a/pint/delegates/formatter/_compound_unit_helpers.py
+++ b/pint/delegates/formatter/_compound_unit_helpers.py
@@ -26,7 +26,7 @@
 )
 
 from ...compat import babel_parse
-from ...util import UnitsContainer
+from ...util import NonReducingUnitsContainer, UnitsContainer
 
 T = TypeVar("T")
 U = TypeVar("U")
@@ -250,6 +250,8 @@ def prepare_compount_unit(
 
     if isinstance(unit, UnitsContainer):
         out = unit.items()
+    elif hasattr(unit, "_units") and isinstance(unit._units, NonReducingUnitsContainer):
+        out = unit._units.non_reduced_d_items
     elif hasattr(unit, "_units"):
         out = unit._units.items()
     else:
diff --git a/pint/delegates/formatter/full.py b/pint/delegates/formatter/full.py
index e6d0eee47..92609b713 100644
--- a/pint/delegates/formatter/full.py
+++ b/pint/delegates/formatter/full.py
@@ -16,7 +16,7 @@
 
 from ..._typing import Magnitude
 from ...compat import Unpack, babel_parse
-from ...util import iterable
+from ...util import NonReducingUnitsContainer, iterable
 from ._compound_unit_helpers import BabelKwds, SortFunc, sort_by_unit_name
 from ._to_register import REGISTERED_FORMATTERS
 from .html import HTMLFormatter
@@ -40,6 +40,11 @@
     from ...registry import UnitRegistry
 
 
+def _sort_func(items, registry):
+    # print([i for i in items])
+    return items
+
+
 class FullFormatter(BaseFormatter):
     """A formatter that dispatch to other formatters.
 
@@ -126,6 +131,8 @@ def format_unit(
     ) -> str:
         uspec = uspec or self.default_format
         sort_func = sort_func or self.default_sort_func
+        if isinstance(unit._units, NonReducingUnitsContainer):
+            sort_func = _sort_func
         return self.get_formatter(uspec).format_unit(
             unit, uspec, sort_func=sort_func, **babel_kwds
         )
diff --git a/pint/delegates/formatter/html.py b/pint/delegates/formatter/html.py
index b8e3f517f..a29ffa5b1 100644
--- a/pint/delegates/formatter/html.py
+++ b/pint/delegates/formatter/html.py
@@ -104,7 +104,9 @@ def format_unit(
             division_fmt = localize_per(length, babel_kwds.get("locale"), "{}/{}")
         else:
             division_fmt = "{}/{}"
+        import pdb
 
+        pdb.set_trace()
         return formatter(
             numerator,
             denominator,
diff --git a/pint/facets/plain/registry.py b/pint/facets/plain/registry.py
index 6e9a43bc6..22898e1d6 100644
--- a/pint/facets/plain/registry.py
+++ b/pint/facets/plain/registry.py
@@ -63,7 +63,7 @@
 from ...errors import DimensionalityError, RedefinitionError, UndefinedUnitError
 from ...pint_eval import build_eval_tree
 from ...util import (
-    NonReducingUnitContainer,
+    NonReducingUnitsContainer,
     ParserHelper,
     UnitsContainer,
     _is_dim,
@@ -1407,8 +1407,8 @@ def UnitsContainer(self, *args: Any, **kwargs: Any) -> UnitsContainer:
 
     __call__ = parse_expression
 
-    def NonReducingUnitContainer(self, units) -> UnitsContainer:
-        return NonReducingUnitContainer(units)
+    def NonReducingUnitsContainer(self, units) -> UnitsContainer:
+        return NonReducingUnitsContainer(units)
 
 
 class PlainRegistry(GenericPlainRegistry[PlainQuantity[Any], PlainUnit]):
diff --git a/pint/testsuite/test_unit.py b/pint/testsuite/test_unit.py
index 2156bbafd..d7c8f2034 100644
--- a/pint/testsuite/test_unit.py
+++ b/pint/testsuite/test_unit.py
@@ -832,6 +832,19 @@ def test_case_sensitivity(self):
         assert ureg.parse_units("j", case_sensitive=False) == UnitsContainer(joule=1)
 
 
+class TestNonReducing(QuantityTestCase):
+    def test_init(self):
+        ureg = self.ureg
+        NRUC_ = ureg.NonReducingUnitsContainer
+
+        mm_per_mm_unit = NRUC_([(ureg.mm, 1), (ureg.mm, -1)])
+        assert mm_per_mm_unit.non_reduced_units == [
+            ureg.UnitsContainer({"millimeter": 1}),
+            ureg.UnitsContainer({"millimeter": -1}),
+        ]
+        assert mm_per_mm_unit == ureg.dimensionless
+
+
 class TestCaseInsensitiveRegistry(QuantityTestCase):
     kwargs = dict(case_sensitive=False)
 
diff --git a/pint/util.py b/pint/util.py
index f8e851451..1f8e0da9d 100644
--- a/pint/util.py
+++ b/pint/util.py
@@ -676,26 +676,46 @@ def _normalize_nonfloat_value(self, value: Scalar) -> Scalar:
         return value
 
 
-class NonReducingUnitContainer(UnitsContainer):
-    """The NonReducingUnitContainer stores UnitsContainers without simplifying common units.
+class NonReducingUnitsContainer(UnitsContainer):
+    """The NonReducingUnitsContainer stores UnitsContainers without simplifying common units.
     This is useful when it is desired to show a unit in the numerator and denominator, eg mm/mm.
     """
 
     def __init__(
         self, units: list[UnitsContainer] | list[tuple[QuantityOrUnitLike, Scalar]]
     ) -> None:
-        if all(isinstance(u, tuple) for u in units):
-            units = [u[0]._units ** u[1] for u in units]
+        self.non_reduced_units = []
 
-        self.non_reduced_units = units
+        for u in units:
+            if isinstance(u, tuple):
+                u = u[0]._units ** u[1]
+            if hasattr(u, "_units"):
+                u = u._units
+            self.non_reduced_units.append(u)
 
         self.reduced_units = UnitsContainer()
-        for unit in units:
+        for unit in self.non_reduced_units:
             self.reduced_units *= unit
 
         self._d = self.reduced_units._d
         self._hash = self.reduced_units._hash
 
+        self.non_reduced_d_items = [
+            (key, value)
+            for uc in self.non_reduced_units
+            for key, value in uc._d.items()
+        ]
+        self.i = 0
+
+    def __repr__(self) -> str:
+        tmp = "[%s]" % ", ".join(
+            [f"'{key}': {value}" for key, value in self.non_reduced_d_items]
+        )
+        return f"<NonReducingUnitsContainer({tmp})>"
+
+    def unit_items(self) -> Iterable[tuple[str, Scalar]]:
+        return [items for _d in self.non_reduced_units for items in _d.items()]
+
 
 class ParserHelper(UnitsContainer):
     """The ParserHelper stores in place the product of variables and

From 6c89e09169825a805575561f1e36bb2063149721 Mon Sep 17 00:00:00 2001
From: andrewgsavage <andrewgsavage@gmail.com>
Date: Tue, 11 Jun 2024 20:36:20 +0100
Subject: [PATCH 05/11] format

---
 pint/delegates/formatter/_format_helpers.py | 5 ++++-
 pint/delegates/formatter/full.py            | 6 +++++-
 pint/delegates/formatter/plain.py           | 9 +++++++++
 3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/pint/delegates/formatter/_format_helpers.py b/pint/delegates/formatter/_format_helpers.py
index 995159e65..501c72c7a 100644
--- a/pint/delegates/formatter/_format_helpers.py
+++ b/pint/delegates/formatter/_format_helpers.py
@@ -161,6 +161,7 @@ def formatter(
     power_fmt: str = "{} ** {}",
     parentheses_fmt: str = "({0})",
     exp_call: FORMATTER = "{:n}".format,
+    empty_numerator_fmt = "1",
 ) -> str:
     """Format a list of (name, exponent) pairs.
 
@@ -183,6 +184,8 @@ def formatter(
         the format used for parenthesis. (Default value = "({0})")
     exp_call : callable
          (Default value = lambda x: f"{x:n}")
+    empty_numerator_fmt : str
+        the format used for an empty numerator. (Default value = "1")
 
     Returns
     -------
@@ -218,7 +221,7 @@ def formatter(
         return join_u(product_fmt, pos_terms + neg_terms)
 
     # Show as Ratio: positive terms / negative terms
-    pos_ret = join_u(product_fmt, pos_terms) or "1"
+    pos_ret = join_u(product_fmt, pos_terms) or empty_numerator_fmt
 
     if not neg_terms:
         return pos_ret
diff --git a/pint/delegates/formatter/full.py b/pint/delegates/formatter/full.py
index 92609b713..c3bf49ef4 100644
--- a/pint/delegates/formatter/full.py
+++ b/pint/delegates/formatter/full.py
@@ -131,10 +131,14 @@ def format_unit(
     ) -> str:
         uspec = uspec or self.default_format
         sort_func = sort_func or self.default_sort_func
+        empty_numerator_fmt = "1"
         if isinstance(unit._units, NonReducingUnitsContainer):
             sort_func = _sort_func
+            empty_numerator_fmt = ""
         return self.get_formatter(uspec).format_unit(
-            unit, uspec, sort_func=sort_func, **babel_kwds
+            unit, uspec, sort_func=sort_func, 
+                        empty_numerator_fmt = empty_numerator_fmt,
+**babel_kwds
         )
 
     def format_quantity(
diff --git a/pint/delegates/formatter/plain.py b/pint/delegates/formatter/plain.py
index d40ec1ae0..d03c00959 100644
--- a/pint/delegates/formatter/plain.py
+++ b/pint/delegates/formatter/plain.py
@@ -81,6 +81,7 @@ def format_unit(
         unit: PlainUnit | Iterable[tuple[str, Any]],
         uspec: str = "",
         sort_func: SortFunc | None = None,
+        empty_numerator_fmt = "1",
         **babel_kwds: Unpack[BabelKwds],
     ) -> str:
         """Format a unit (can be compound) into string
@@ -203,6 +204,7 @@ def format_unit(
         unit: PlainUnit | Iterable[tuple[str, Any]],
         uspec: str = "",
         sort_func: SortFunc | None = None,
+        empty_numerator_fmt = "1",
         **babel_kwds: Unpack[BabelKwds],
     ) -> str:
         numerator, denominator = prepare_compount_unit(
@@ -225,6 +227,7 @@ def format_unit(
             division_fmt=division_fmt,
             power_fmt="{}**{}",
             parentheses_fmt=r"({})",
+            empty_numerator_fmt=empty_numerator_fmt,
         )
 
     def format_quantity(
@@ -313,12 +316,16 @@ def format_unit(
         unit: PlainUnit | Iterable[tuple[str, Any]],
         uspec: str = "",
         sort_func: SortFunc | None = None,
+                                        empty_numerator_fmt="1",
+
         **babel_kwds: Unpack[BabelKwds],
+
     ) -> str:
         numerator, denominator = prepare_compount_unit(
             unit,
             uspec,
             sort_func=sort_func,
+
             **babel_kwds,
             registry=self._registry,
         )
@@ -339,6 +346,8 @@ def format_unit(
             power_fmt="{}{}",
             parentheses_fmt="({})",
             exp_call=pretty_fmt_exponent,
+                        empty_numerator_fmt=empty_numerator_fmt,
+
         )
 
     def format_quantity(

From a0f7a71e066d35c2817348e9d24ee9ad522e4d9b Mon Sep 17 00:00:00 2001
From: Andrew <andrewgsavage@gmail.com>
Date: Thu, 27 Jun 2024 11:50:55 +0100
Subject: [PATCH 06/11] add arg

---
 pint/delegates/formatter/_compound_unit_helpers.py |  1 +
 pint/delegates/formatter/plain.py                  | 12 ++++--------
 2 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/pint/delegates/formatter/_compound_unit_helpers.py b/pint/delegates/formatter/_compound_unit_helpers.py
index c8ac1e2d9..46934c063 100644
--- a/pint/delegates/formatter/_compound_unit_helpers.py
+++ b/pint/delegates/formatter/_compound_unit_helpers.py
@@ -246,6 +246,7 @@ def prepare_compount_unit(
     locale: Locale | str | None = None,
     as_ratio: bool = True,
     registry: UnitRegistry | None = None,
+    empty_numerator_fmt="1",
 ) -> tuple[Iterable[tuple[str, T]], Iterable[tuple[str, T]]]:
     """Format compound unit into unit container given
     an spec and locale.
diff --git a/pint/delegates/formatter/plain.py b/pint/delegates/formatter/plain.py
index d03c00959..5cf77f3e0 100644
--- a/pint/delegates/formatter/plain.py
+++ b/pint/delegates/formatter/plain.py
@@ -81,7 +81,7 @@ def format_unit(
         unit: PlainUnit | Iterable[tuple[str, Any]],
         uspec: str = "",
         sort_func: SortFunc | None = None,
-        empty_numerator_fmt = "1",
+        empty_numerator_fmt="1",
         **babel_kwds: Unpack[BabelKwds],
     ) -> str:
         """Format a unit (can be compound) into string
@@ -204,7 +204,7 @@ def format_unit(
         unit: PlainUnit | Iterable[tuple[str, Any]],
         uspec: str = "",
         sort_func: SortFunc | None = None,
-        empty_numerator_fmt = "1",
+        empty_numerator_fmt="1",
         **babel_kwds: Unpack[BabelKwds],
     ) -> str:
         numerator, denominator = prepare_compount_unit(
@@ -316,16 +316,13 @@ def format_unit(
         unit: PlainUnit | Iterable[tuple[str, Any]],
         uspec: str = "",
         sort_func: SortFunc | None = None,
-                                        empty_numerator_fmt="1",
-
+        empty_numerator_fmt="1",
         **babel_kwds: Unpack[BabelKwds],
-
     ) -> str:
         numerator, denominator = prepare_compount_unit(
             unit,
             uspec,
             sort_func=sort_func,
-
             **babel_kwds,
             registry=self._registry,
         )
@@ -346,8 +343,7 @@ def format_unit(
             power_fmt="{}{}",
             parentheses_fmt="({})",
             exp_call=pretty_fmt_exponent,
-                        empty_numerator_fmt=empty_numerator_fmt,
-
+            empty_numerator_fmt=empty_numerator_fmt,
         )
 
     def format_quantity(

From bcec387b40ff966148062de63306251bb158dd04 Mon Sep 17 00:00:00 2001
From: Andrew <andrewgsavage@gmail.com>
Date: Thu, 27 Jun 2024 11:53:19 +0100
Subject: [PATCH 07/11] lint

---
 pint/delegates/formatter/_format_helpers.py | 2 +-
 pint/delegates/formatter/full.py            | 8 +++++---
 2 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/pint/delegates/formatter/_format_helpers.py b/pint/delegates/formatter/_format_helpers.py
index 065263126..429c0ba5f 100644
--- a/pint/delegates/formatter/_format_helpers.py
+++ b/pint/delegates/formatter/_format_helpers.py
@@ -163,7 +163,7 @@ def formatter(
     power_fmt: str = "{} ** {}",
     parentheses_fmt: str = "({0})",
     exp_call: FORMATTER = "{:n}".format,
-    empty_numerator_fmt = "1",
+    empty_numerator_fmt="1",
 ) -> str:
     """Format a list of (name, exponent) pairs.
 
diff --git a/pint/delegates/formatter/full.py b/pint/delegates/formatter/full.py
index 8a633b4c7..5133e0691 100644
--- a/pint/delegates/formatter/full.py
+++ b/pint/delegates/formatter/full.py
@@ -144,9 +144,11 @@ def format_unit(
             sort_func = _sort_func
             empty_numerator_fmt = ""
         return self.get_formatter(uspec).format_unit(
-            unit, uspec, sort_func=sort_func, 
-                        empty_numerator_fmt = empty_numerator_fmt,
-**babel_kwds
+            unit,
+            uspec,
+            sort_func=sort_func,
+            empty_numerator_fmt=empty_numerator_fmt,
+            **babel_kwds,
         )
 
     def format_quantity(

From 315a9970ba52b435ad7f59c4db99902709baf3e0 Mon Sep 17 00:00:00 2001
From: Andrew <andrewgsavage@gmail.com>
Date: Thu, 27 Jun 2024 11:54:06 +0100
Subject: [PATCH 08/11] lint

---
 pint/delegates/formatter/html.py | 2 --
 1 file changed, 2 deletions(-)

diff --git a/pint/delegates/formatter/html.py b/pint/delegates/formatter/html.py
index a29ffa5b1..b8e3f517f 100644
--- a/pint/delegates/formatter/html.py
+++ b/pint/delegates/formatter/html.py
@@ -104,9 +104,7 @@ def format_unit(
             division_fmt = localize_per(length, babel_kwds.get("locale"), "{}/{}")
         else:
             division_fmt = "{}/{}"
-        import pdb
 
-        pdb.set_trace()
         return formatter(
             numerator,
             denominator,

From 5fdf45def5998abf48b48ae43e7f6931abe1b708 Mon Sep 17 00:00:00 2001
From: Andrew <andrewgsavage@gmail.com>
Date: Sat, 29 Jun 2024 18:14:43 +0100
Subject: [PATCH 09/11] add reg flag, tests

---
 pint/facets/plain/registry.py | 23 ++++++++++++++++++-----
 pint/registry.py              |  2 ++
 pint/testsuite/test_unit.py   | 12 ++++++++++++
 pint/util.py                  | 33 +++++++++++++++++++++++++++------
 4 files changed, 59 insertions(+), 11 deletions(-)

diff --git a/pint/facets/plain/registry.py b/pint/facets/plain/registry.py
index 22898e1d6..7f5a499d3 100644
--- a/pint/facets/plain/registry.py
+++ b/pint/facets/plain/registry.py
@@ -218,6 +218,7 @@ def __init__(
         force_ndarray: bool = False,
         force_ndarray_like: bool = False,
         on_redefinition: str = "warn",
+        auto_reduce_units: bool = True,
         auto_reduce_dimensions: bool = False,
         autoconvert_to_preferred: bool = False,
         preprocessors: list[PreprocessorType] | None = None,
@@ -262,6 +263,9 @@ def __init__(
         #: Action to take in case a unit is redefined. 'warn', 'raise', 'ignore'
         self._on_redefinition = on_redefinition
 
+        #: Determines if units should be reduced on appropriate operations.
+        self.auto_reduce_units = auto_reduce_units
+
         #: Determines if dimensionality should be reduced on appropriate operations.
         self.auto_reduce_dimensions = auto_reduce_dimensions
 
@@ -1259,7 +1263,6 @@ def _parse_units_as_container(
 
         if as_delta:
             cache[input_string] = ret
-
         return ret
 
     def _eval_token(
@@ -1403,12 +1406,22 @@ def _define_op(s: str):
     # TODO: Maybe in the future we need to change it to a more meaningful
     # non-colliding name.
     def UnitsContainer(self, *args: Any, **kwargs: Any) -> UnitsContainer:
-        return UnitsContainer(*args, non_int_type=self.non_int_type, **kwargs)
+        return UnitsContainer(
+            *args,
+            non_int_type=self.non_int_type,
+            auto_reduce_units=self.auto_reduce_units,
+            **kwargs,
+        )
 
-    __call__ = parse_expression
+    def NonReducingUnitsContainer(self, *args: Any, **kwargs: Any) -> UnitsContainer:
+        return NonReducingUnitsContainer(
+            *args,
+            non_int_type=self.non_int_type,
+            auto_reduce_units=self.auto_reduce_units,
+            **kwargs,
+        )
 
-    def NonReducingUnitsContainer(self, units) -> UnitsContainer:
-        return NonReducingUnitsContainer(units)
+    __call__ = parse_expression
 
 
 class PlainRegistry(GenericPlainRegistry[PlainQuantity[Any], PlainUnit]):
diff --git a/pint/registry.py b/pint/registry.py
index ceb9b62d1..c0c0e96ce 100644
--- a/pint/registry.py
+++ b/pint/registry.py
@@ -120,6 +120,7 @@ def __init__(
         autoconvert_offset_to_baseunit: bool = False,
         on_redefinition: str = "warn",
         system=None,
+        auto_reduce_units=True,
         auto_reduce_dimensions=False,
         autoconvert_to_preferred=False,
         preprocessors=None,
@@ -136,6 +137,7 @@ def __init__(
             default_as_delta=default_as_delta,
             autoconvert_offset_to_baseunit=autoconvert_offset_to_baseunit,
             system=system,
+            auto_reduce_units=auto_reduce_units,
             auto_reduce_dimensions=auto_reduce_dimensions,
             autoconvert_to_preferred=autoconvert_to_preferred,
             preprocessors=preprocessors,
diff --git a/pint/testsuite/test_unit.py b/pint/testsuite/test_unit.py
index d7c8f2034..4921ef3ad 100644
--- a/pint/testsuite/test_unit.py
+++ b/pint/testsuite/test_unit.py
@@ -844,6 +844,18 @@ def test_init(self):
         ]
         assert mm_per_mm_unit == ureg.dimensionless
 
+    def test_ureg_auto_reduce_units(self):
+        ureg = UnitRegistry(auto_reduce_units=False)
+        NRUC_ = ureg.NonReducingUnitsContainer
+
+        ureg.Unit("mm") / ureg.Unit("mm") == NRUC_([(ureg.mm, 1), (ureg.mm, -1)])
+
+    def test_formatting(self):
+        ureg = UnitRegistry(auto_reduce_units=False)
+        u = ureg.Unit("mm") / ureg.Unit("mm")
+        assert format(u, "~D") == "mm / mm"
+        assert format(u, "P") == "millimeter/millimeter"
+
 
 class TestCaseInsensitiveRegistry(QuantityTestCase):
     kwargs = dict(case_sensitive=False)
diff --git a/pint/util.py b/pint/util.py
index 1f8e0da9d..9e2dc5b07 100644
--- a/pint/util.py
+++ b/pint/util.py
@@ -442,15 +442,20 @@ class UnitsContainer(Mapping[str, Scalar]):
         Numerical type used for non integer values.
     """
 
-    __slots__ = ("_d", "_hash", "_one", "_non_int_type")
+    __slots__ = ("_d", "_hash", "_one", "_non_int_type", "_auto_reduce_units")
 
     _d: udict
     _hash: int | None
     _one: Scalar
     _non_int_type: type
+    _auto_reduce_units: bool
 
     def __init__(
-        self, *args: Any, non_int_type: type | None = None, **kwargs: Any
+        self,
+        *args: Any,
+        non_int_type: type | None = None,
+        auto_reduce_units: bool = True,
+        **kwargs: Any,
     ) -> None:
         if args and isinstance(args[0], UnitsContainer):
             default_non_int_type = args[0]._non_int_type
@@ -458,6 +463,7 @@ def __init__(
             default_non_int_type = float
 
         self._non_int_type = non_int_type or default_non_int_type
+        self._auto_reduce_units = auto_reduce_units
 
         if self._non_int_type is float:
             self._one = 1
@@ -620,13 +626,20 @@ def __copy__(self):
         out._hash = self._hash
         out._non_int_type = self._non_int_type
         out._one = self._one
+        out._auto_reduce_units = self._auto_reduce_units
         return out
 
+    def __deepcopy__(self, memo):
+        return self.copy()
+
     def __mul__(self, other: Any):
-        if not isinstance(other, self.__class__):
+        if not isinstance(other, UnitsContainer):
             err = "Cannot multiply UnitsContainer by {}"
             raise TypeError(err.format(type(other)))
 
+        if not self._auto_reduce_units:
+            return NonReducingUnitsContainer([self, other])
+
         new = self.copy()
         for key, value in other.items():
             new._d[key] += value
@@ -650,10 +663,13 @@ def __pow__(self, other: Any):
         return new
 
     def __truediv__(self, other: Any):
-        if not isinstance(other, self.__class__):
+        if not isinstance(other, UnitsContainer):
             err = "Cannot divide UnitsContainer by {}"
             raise TypeError(err.format(type(other)))
 
+        if not self._auto_reduce_units:
+            return NonReducingUnitsContainer([self, UnitsContainer({}) / other])
+
         new = self.copy()
         for key, value in other.items():
             new._d[key] -= self._normalize_nonfloat_value(value)
@@ -664,7 +680,7 @@ def __truediv__(self, other: Any):
         return new
 
     def __rtruediv__(self, other: Any):
-        if not isinstance(other, self.__class__) and other != 1:
+        if not isinstance(other, UnitsContainer) and other != 1:
             err = "Cannot divide {} by UnitsContainer"
             raise TypeError(err.format(type(other)))
 
@@ -682,9 +698,14 @@ class NonReducingUnitsContainer(UnitsContainer):
     """
 
     def __init__(
-        self, units: list[UnitsContainer] | list[tuple[QuantityOrUnitLike, Scalar]]
+        self,
+        units: list[UnitsContainer] | list[tuple[QuantityOrUnitLike, Scalar]],
+        non_int_type: type | None = None,
+        auto_reduce_units: bool = True,
     ) -> None:
         self.non_reduced_units = []
+        self._non_int_type = non_int_type
+        self.auto_reduce_units = auto_reduce_units
 
         for u in units:
             if isinstance(u, tuple):

From 3e5bfba1998989c2ecedd56452ffc85fb8ab342d Mon Sep 17 00:00:00 2001
From: Andrew <andrewgsavage@gmail.com>
Date: Sat, 29 Jun 2024 20:35:42 +0100
Subject: [PATCH 10/11] add reg flag, tests

---
 pint/testsuite/test_unit.py | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/pint/testsuite/test_unit.py b/pint/testsuite/test_unit.py
index 4921ef3ad..7ce1a84e4 100644
--- a/pint/testsuite/test_unit.py
+++ b/pint/testsuite/test_unit.py
@@ -837,24 +837,29 @@ def test_init(self):
         ureg = self.ureg
         NRUC_ = ureg.NonReducingUnitsContainer
 
-        mm_per_mm_unit = NRUC_([(ureg.mm, 1), (ureg.mm, -1)])
-        assert mm_per_mm_unit.non_reduced_units == [
+        strain_unit_container = NRUC_([(ureg.mm, 1), (ureg.mm, -1)])
+        assert strain_unit_container.non_reduced_units == [
             ureg.UnitsContainer({"millimeter": 1}),
             ureg.UnitsContainer({"millimeter": -1}),
         ]
-        assert mm_per_mm_unit == ureg.dimensionless
+        assert strain_unit_container == ureg.dimensionless
 
     def test_ureg_auto_reduce_units(self):
         ureg = UnitRegistry(auto_reduce_units=False)
         NRUC_ = ureg.NonReducingUnitsContainer
 
-        ureg.Unit("mm") / ureg.Unit("mm") == NRUC_([(ureg.mm, 1), (ureg.mm, -1)])
+        strain_unit = ureg.Unit("mm") / ureg.Unit("mm")
+        strain_unit == NRUC_([(ureg.mm, 1), (ureg.mm, -1)])
+        strain_unit == ureg.Unit("dimensionless")
+
+        strain_q = ureg.Quantity(1, "mm") / ureg.Quantity(1, "mm")
+        assert strain_q.units == strain_unit
 
     def test_formatting(self):
         ureg = UnitRegistry(auto_reduce_units=False)
-        u = ureg.Unit("mm") / ureg.Unit("mm")
-        assert format(u, "~D") == "mm / mm"
-        assert format(u, "P") == "millimeter/millimeter"
+        strain_unit = ureg.Unit("mm") / ureg.Unit("mm")
+        assert format(strain_unit, "~D") == "mm / mm"
+        assert format(strain_unit, "P") == "millimeter/millimeter"
 
 
 class TestCaseInsensitiveRegistry(QuantityTestCase):

From af3cd64a5382d2ea67edafb1bb2acbe0de3982d7 Mon Sep 17 00:00:00 2001
From: andrewgsavage <andrewgsavage@gmail.com>
Date: Thu, 26 Feb 2026 21:28:35 +0000
Subject: [PATCH 11/11] Update pint/util.py

Co-authored-by: mutricyl <118692416+mutricyl@users.noreply.github.com>
---
 pint/util.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pint/util.py b/pint/util.py
index 9e2dc5b07..ed20aad99 100644
--- a/pint/util.py
+++ b/pint/util.py
@@ -705,7 +705,7 @@ def __init__(
     ) -> None:
         self.non_reduced_units = []
         self._non_int_type = non_int_type
-        self.auto_reduce_units = auto_reduce_units
+        self._auto_reduce_units = auto_reduce_units
 
         for u in units:
             if isinstance(u, tuple):