From 9320a32227bb0a8e5ab45bf81a25ea311d8cbdba Mon Sep 17 00:00:00 2001
From: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
Date: Sun, 22 Oct 2023 10:48:35 -0400
Subject: [PATCH 01/13] Implement sorting units by dimension order

Once upon a time, ISO 80000 attempted to codify preferences for ordering units when describing quantities, for example `kW h` (not `h Kw`).  While they have withdrawn the standard, there are many publications that state a preference for ordering units when describing quantities.

Pint allows users to choose to sort units alphabetically or not (thus `kW * h` becomes `h * kW`, whereas `kW * s` retmains `kW * s` becase `kW` sorts as less than `s`).

This PR adds a `sort_dims` parameter to `pint.formatting.formatter` which can be used in conjunction with alphabetical sorting.  `sort_dims` imposes a "most significant dimension" order on the units, which are then sorted alphebetically (or not) within each dimension type.

This addresses #1841.  It is intended as a prototype to evaluate as pint's formatting roadmap evolves.  In particular, it needs a way to make `sort_dims` more accessible to the user.

Signed-off-by: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
---
 pint/formatting.py            | 61 +++++++++++++++++++++++++++++++++++
 pint/testsuite/test_issues.py | 17 ++++++++++
 2 files changed, 78 insertions(+)

diff --git a/pint/formatting.py b/pint/formatting.py
index b00b771c7..d259ab615 100644
--- a/pint/formatting.py
+++ b/pint/formatting.py
@@ -197,6 +197,7 @@ def format_pretty(unit: UnitsContainer, registry: UnitRegistry, **options) -> st
         power_fmt="{}{}",
         parentheses_fmt="({})",
         exp_call=_pretty_fmt_exponent,
+        registry=registry,
         **options,
     )
 
@@ -228,6 +229,7 @@ def format_latex(unit: UnitsContainer, registry: UnitRegistry, **options) -> str
         division_fmt=r"\frac[{}][{}]",
         power_fmt="{}^[{}]",
         parentheses_fmt=r"\left({}\right)",
+        registry=registry,
         **options,
     )
     return formatted.replace("[", "{").replace("]", "}")
@@ -259,6 +261,7 @@ def format_html(unit: UnitsContainer, registry: UnitRegistry, **options) -> str:
         division_fmt=r"{}/{}",
         power_fmt=r"{}<sup>{}</sup>",
         parentheses_fmt=r"({})",
+        registry=registry,
         **options,
     )
 
@@ -273,6 +276,7 @@ def format_default(unit: UnitsContainer, registry: UnitRegistry, **options) -> s
         division_fmt=" / ",
         power_fmt="{} ** {}",
         parentheses_fmt=r"({})",
+        registry=registry,
         **options,
     )
 
@@ -287,10 +291,53 @@ def format_compact(unit: UnitsContainer, registry: UnitRegistry, **options) -> s
         division_fmt="/",
         power_fmt="{}**{}",
         parentheses_fmt=r"({})",
+        registry=registry,
         **options,
     )
 
 
+dim_order = [ '[substance]', '[mass]', '[current]', '[luminosity]', '[length]', '[time]', '[temperature]' ]
+def dim_sort(units: Iterable[list[str]], registry: UnitRegistry):
+    """Sort a list of units by dimensional order.
+
+    Parameters
+    ----------
+    units : list
+        a list of unit names (without values).
+    registry : UnitRegistry
+        the registry to use for looking up the dimensions of each unit.
+
+    Returns
+    -------
+    list
+        the list of units sorted by most significant dimension first.
+
+    Raises
+    ------
+    KeyError
+        If unit cannot be found in the registry.
+    """
+    ret_dict = dict()
+    many = len(units) > 1
+    for name in units:
+        cname = registry.get_name(name)
+        if not cname:
+            continue
+        dim_types = iter(dim_order)
+        while True:
+            try:
+                dim = next(dim_types)
+                if dim in registry.get_dimensionality(cname):
+                    if dim not in ret_dict:
+                        ret_dict[dim] = list()
+                    ret_dict[dim].append(cname)
+                    break
+            except StopIteration:
+                raise KeyError(f"Unit {cname} has no recognized dimensions")
+
+    ret = sum([ret_dict[dim] for dim in dim_order if dim in ret_dict], [])
+    return ret
+
 def formatter(
     items: Iterable[tuple[str, Number]],
     as_ratio: bool = True,
@@ -304,6 +351,8 @@ def formatter(
     babel_length: str = "long",
     babel_plural_form: str = "one",
     sort: bool = True,
+    sort_dims: bool = False,
+    registry: Optional[UnitRegistry] = None,
 ) -> str:
     """Format a list of (name, exponent) pairs.
 
@@ -334,6 +383,12 @@ def formatter(
          (Default value = lambda x: f"{x:n}")
     sort : bool, optional
         True to sort the formatted units alphabetically (Default value = True)
+    sort_dims : bool, optional
+        True to sort the units dimentionally (Default value = False).
+        When dimensions have multiple units, sort by "most significant dimension" the unit contains
+        When both `sort` and `sort_dims` are True, sort alphabetically within sorted dimensions
+    registry : UnitRegistry, optional
+        The registry to use if `sort_dims` is True
 
     Returns
     -------
@@ -393,6 +448,12 @@ def formatter(
         else:
             neg_terms.append(power_fmt.format(key, fun(value)))
 
+    if sort_dims:
+        if len(pos_terms)>1:
+            pos_terms = dim_sort(pos_terms, registry)
+        if len(neg_terms)>1:
+            neg_terms = dim_sort(neg_terms, registry)
+
     if not as_ratio:
         # Show as Product: positive * negative terms ** -1
         return _join(product_fmt, pos_terms + neg_terms)
diff --git a/pint/testsuite/test_issues.py b/pint/testsuite/test_issues.py
index c98ac61bf..c4bdd2b5d 100644
--- a/pint/testsuite/test_issues.py
+++ b/pint/testsuite/test_issues.py
@@ -1150,3 +1150,20 @@ def test_issues_1505():
     assert isinstance(
         ur.Quantity("m/s").magnitude, decimal.Decimal
     )  # unexpected fail (magnitude should be a decimal)
+
+
+def test_issues_1841():
+    import pint
+
+    # sets compact display mode
+    ur = UnitRegistry()
+    ur.default_format = '~P'
+
+    # creates quantity
+    q = ur.Quantity("1 kW * 1 h")
+
+    assert pint.formatting.format_unit(q.u._units, spec='', registry=ur, sort_dims=True) == 'kilowatt * hour'
+    assert pint.formatting.format_unit(q.u._units, spec='', registry=ur, sort_dims=False) == 'hour * kilowatt'
+
+    # this prints "1 h·kW", not "1 kW·h" unless sort_dims is True
+    # print(q)

From cdf7e6541149e9e1dd3f9626716675bc5265abda Mon Sep 17 00:00:00 2001
From: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
Date: Sun, 22 Oct 2023 10:52:31 -0400
Subject: [PATCH 02/13] pre-commit fixes

Forgot to run pre-commit for initial commit.

Signed-off-by: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
---
 pint/formatting.py            | 19 +++++++++++++++----
 pint/testsuite/test_issues.py | 12 +++++++++---
 2 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/pint/formatting.py b/pint/formatting.py
index d259ab615..90613d997 100644
--- a/pint/formatting.py
+++ b/pint/formatting.py
@@ -296,7 +296,17 @@ def format_compact(unit: UnitsContainer, registry: UnitRegistry, **options) -> s
     )
 
 
-dim_order = [ '[substance]', '[mass]', '[current]', '[luminosity]', '[length]', '[time]', '[temperature]' ]
+dim_order = [
+    "[substance]",
+    "[mass]",
+    "[current]",
+    "[luminosity]",
+    "[length]",
+    "[time]",
+    "[temperature]",
+]
+
+
 def dim_sort(units: Iterable[list[str]], registry: UnitRegistry):
     """Sort a list of units by dimensional order.
 
@@ -318,7 +328,7 @@ def dim_sort(units: Iterable[list[str]], registry: UnitRegistry):
         If unit cannot be found in the registry.
     """
     ret_dict = dict()
-    many = len(units) > 1
+    len(units) > 1
     for name in units:
         cname = registry.get_name(name)
         if not cname:
@@ -338,6 +348,7 @@ def dim_sort(units: Iterable[list[str]], registry: UnitRegistry):
     ret = sum([ret_dict[dim] for dim in dim_order if dim in ret_dict], [])
     return ret
 
+
 def formatter(
     items: Iterable[tuple[str, Number]],
     as_ratio: bool = True,
@@ -449,9 +460,9 @@ def formatter(
             neg_terms.append(power_fmt.format(key, fun(value)))
 
     if sort_dims:
-        if len(pos_terms)>1:
+        if len(pos_terms) > 1:
             pos_terms = dim_sort(pos_terms, registry)
-        if len(neg_terms)>1:
+        if len(neg_terms) > 1:
             neg_terms = dim_sort(neg_terms, registry)
 
     if not as_ratio:
diff --git a/pint/testsuite/test_issues.py b/pint/testsuite/test_issues.py
index c4bdd2b5d..3ee0f11df 100644
--- a/pint/testsuite/test_issues.py
+++ b/pint/testsuite/test_issues.py
@@ -1157,13 +1157,19 @@ def test_issues_1841():
 
     # sets compact display mode
     ur = UnitRegistry()
-    ur.default_format = '~P'
+    ur.default_format = "~P"
 
     # creates quantity
     q = ur.Quantity("1 kW * 1 h")
 
-    assert pint.formatting.format_unit(q.u._units, spec='', registry=ur, sort_dims=True) == 'kilowatt * hour'
-    assert pint.formatting.format_unit(q.u._units, spec='', registry=ur, sort_dims=False) == 'hour * kilowatt'
+    assert (
+        pint.formatting.format_unit(q.u._units, spec="", registry=ur, sort_dims=True)
+        == "kilowatt * hour"
+    )
+    assert (
+        pint.formatting.format_unit(q.u._units, spec="", registry=ur, sort_dims=False)
+        == "hour * kilowatt"
+    )
 
     # this prints "1 h·kW", not "1 kW·h" unless sort_dims is True
     # print(q)

From 1d7327a850aa8fdce71edfe936cadf7ad4f65296 Mon Sep 17 00:00:00 2001
From: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
Date: Sun, 22 Oct 2023 17:34:28 -0400
Subject: [PATCH 03/13] Make sort_dims default and sorting user-defineable

Per suggestions from @andrewgsavage make `sort_dims` default.  Also allow users to specify dimensional sorting in registry definition.

Also fix a number of sub-tests not previously tested.  Tests all pass without any drama.

Signed-off-by: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
---
 CHANGES                          |  2 +
 pint/default_en.txt              |  1 +
 pint/facets/plain/definitions.py |  6 ++-
 pint/formatting.py               | 79 +++++++++++++++++++-------------
 pint/testsuite/test_issues.py    | 54 ++++++++++++++++++++++
 5 files changed, 109 insertions(+), 33 deletions(-)

diff --git a/CHANGES b/CHANGES
index 1cde05402..0b8d625d3 100644
--- a/CHANGES
+++ b/CHANGES
@@ -4,6 +4,8 @@ Pint Changelog
 0.23 (unreleased)
 -----------------
 
+- Add `dim_sort` parameter to formatter.
+  (PR #1864, fixes Issue #1841)
 - Fixed Transformation type protocol.
   (PR #1805, PR #1832)
 - Documented to_preferred and created added an autoautoconvert_to_preferred registry option.
diff --git a/pint/default_en.txt b/pint/default_en.txt
index 5fc7f8265..391eeb37a 100644
--- a/pint/default_en.txt
+++ b/pint/default_en.txt
@@ -56,6 +56,7 @@
 @defaults
     group = international
     system = mks
+    dim_order = [ "[substance]", "[mass]", "[current]", "[luminosity]", "[length]", "[]", "[time]", "[temperature]", ]
 @end
 
 
diff --git a/pint/facets/plain/definitions.py b/pint/facets/plain/definitions.py
index 44bf29858..05cb055a0 100644
--- a/pint/facets/plain/definitions.py
+++ b/pint/facets/plain/definitions.py
@@ -11,9 +11,10 @@
 import itertools
 import numbers
 import typing as ty
+import ast
 from dataclasses import dataclass
 from functools import cached_property
-from typing import Any, Optional
+from typing import Any, List, Optional
 
 from ..._typing import Magnitude
 from ... import errors
@@ -60,12 +61,15 @@ class DefaultsDefinition:
 
     group: ty.Optional[str]
     system: ty.Optional[str]
+    dim_order: ty.Optional[List[str]]
 
     def items(self):
         if self.group is not None:
             yield "group", self.group
         if self.system is not None:
             yield "system", self.system
+        if self.dim_order is not None:
+            yield "dim_order", ast.literal_eval(self.dim_order)
 
 
 @dataclass(frozen=True)
diff --git a/pint/formatting.py b/pint/formatting.py
index 90613d997..b158da623 100644
--- a/pint/formatting.py
+++ b/pint/formatting.py
@@ -13,7 +13,8 @@
 import functools
 import re
 import warnings
-from typing import Callable, Any, TYPE_CHECKING, TypeVar, Optional, Union
+from typing import Callable, Any, TYPE_CHECKING, TypeVar, List, Optional, Tuple, Union
+from collections import OrderedDict
 from collections.abc import Iterable
 from numbers import Number
 
@@ -220,7 +221,18 @@ def latex_escape(string: str) -> str:
 
 @register_unit_format("L")
 def format_latex(unit: UnitsContainer, registry: UnitRegistry, **options) -> str:
-    preprocessed = {rf"\mathrm{{{latex_escape(u)}}}": p for u, p in unit.items()}
+    # Lift the sorting by dimensions b/c the preprocessed units are unrecognizeable
+    sorted_units = dim_sort(unit.items(), registry)
+    preprocessed_list = [
+        (
+            rf"\mathrm{{{latex_escape(u)}}}",
+            p,
+        )
+        for u, p in sorted_units
+    ]
+    preprocessed = OrderedDict()
+    for k, v in preprocessed_list:
+        preprocessed[k] = v
     formatted = formatter(
         preprocessed.items(),
         as_ratio=True,
@@ -229,6 +241,8 @@ def format_latex(unit: UnitsContainer, registry: UnitRegistry, **options) -> str
         division_fmt=r"\frac[{}][{}]",
         power_fmt="{}^[{}]",
         parentheses_fmt=r"\left({}\right)",
+        sort=False,
+        sort_dims=False,
         registry=registry,
         **options,
     )
@@ -296,24 +310,13 @@ def format_compact(unit: UnitsContainer, registry: UnitRegistry, **options) -> s
     )
 
 
-dim_order = [
-    "[substance]",
-    "[mass]",
-    "[current]",
-    "[luminosity]",
-    "[length]",
-    "[time]",
-    "[temperature]",
-]
-
-
-def dim_sort(units: Iterable[list[str]], registry: UnitRegistry):
+def dim_sort(items: Iterable[Tuple[str, Number]], registry: UnitRegistry):
     """Sort a list of units by dimensional order.
 
     Parameters
     ----------
-    units : list
-        a list of unit names (without values).
+    items : tuple
+        a list of tuples containing (unit names, exponent values).
     registry : UnitRegistry
         the registry to use for looking up the dimensions of each unit.
 
@@ -327,30 +330,46 @@ def dim_sort(units: Iterable[list[str]], registry: UnitRegistry):
     KeyError
         If unit cannot be found in the registry.
     """
+    if registry is None or len(items) <= 1:
+        return items
+    # if len(items) == 2 and items[0][1] * items[1][1] < 0:
+    #     return items
     ret_dict = dict()
-    len(units) > 1
-    for name in units:
+    for name, value in items:
         cname = registry.get_name(name)
         if not cname:
             continue
-        dim_types = iter(dim_order)
+        cname_dims = registry.get_dimensionality(cname)
+        if len(cname_dims) == 0:
+            cname_dims = {"[]": None}
+        dim_types = iter(registry._defaults["dim_order"])
         while True:
             try:
                 dim = next(dim_types)
-                if dim in registry.get_dimensionality(cname):
+                if dim in cname_dims:
                     if dim not in ret_dict:
                         ret_dict[dim] = list()
-                    ret_dict[dim].append(cname)
+                    ret_dict[dim].append(
+                        (
+                            name,
+                            value,
+                        )
+                    )
                     break
             except StopIteration:
-                raise KeyError(f"Unit {cname} has no recognized dimensions")
+                raise KeyError(
+                    f"Unit {name} (aka {cname}) has no recognized dimensions"
+                )
 
-    ret = sum([ret_dict[dim] for dim in dim_order if dim in ret_dict], [])
+    ret = sum(
+        [ret_dict[dim] for dim in registry._defaults["dim_order"] if dim in ret_dict],
+        [],
+    )
     return ret
 
 
 def formatter(
-    items: Iterable[tuple[str, Number]],
+    items: Iterable[Tuple[str, Number]],
     as_ratio: bool = True,
     single_denominator: bool = False,
     product_fmt: str = " * ",
@@ -362,7 +381,7 @@ def formatter(
     babel_length: str = "long",
     babel_plural_form: str = "one",
     sort: bool = True,
-    sort_dims: bool = False,
+    sort_dims: bool = True,
     registry: Optional[UnitRegistry] = None,
 ) -> str:
     """Format a list of (name, exponent) pairs.
@@ -420,6 +439,8 @@ def formatter(
 
     if sort:
         items = sorted(items)
+    if sort_dims:
+        items = dim_sort(items, registry)
     for key, value in items:
         if locale and babel_length and babel_plural_form and key in _babel_units:
             _key = _babel_units[key]
@@ -459,12 +480,6 @@ def formatter(
         else:
             neg_terms.append(power_fmt.format(key, fun(value)))
 
-    if sort_dims:
-        if len(pos_terms) > 1:
-            pos_terms = dim_sort(pos_terms, registry)
-        if len(neg_terms) > 1:
-            neg_terms = dim_sort(neg_terms, registry)
-
     if not as_ratio:
         # Show as Product: positive * negative terms ** -1
         return _join(product_fmt, pos_terms + neg_terms)
@@ -640,7 +655,7 @@ def vector_to_latex(vec: Iterable[Any], fmtfun: FORMATTER = ".2f".format) -> str
 
 
 def matrix_to_latex(matrix: ItMatrix, fmtfun: FORMATTER = ".2f".format) -> str:
-    ret: list[str] = []
+    ret: List[str] = []
 
     for row in matrix:
         ret += [" & ".join(fmtfun(f) for f in row)]
diff --git a/pint/testsuite/test_issues.py b/pint/testsuite/test_issues.py
index 3ee0f11df..7702ea2eb 100644
--- a/pint/testsuite/test_issues.py
+++ b/pint/testsuite/test_issues.py
@@ -1173,3 +1173,57 @@ def test_issues_1841():
 
     # this prints "1 h·kW", not "1 kW·h" unless sort_dims is True
     # print(q)
+
+    q = ur.Quantity("1 kV * A")
+
+    assert (
+        pint.formatting.format_unit(q.u._units, spec="", registry=ur, sort_dims=True)
+        == "kilovolt * ampere"
+    )
+    assert (
+        pint.formatting.format_unit(q.u._units, spec="", registry=ur, sort_dims=False)
+        == "ampere * kilovolt"
+    )
+
+    # this prints "1 A·kV", not "1 kV·A" unless sort_dims is True
+    # print(q)
+
+    q = ur.Quantity("1 N * m")
+
+    assert (
+        pint.formatting.format_unit(q.u._units, spec="", registry=ur, sort_dims=True)
+        == "newton * meter"
+    )
+    assert (
+        pint.formatting.format_unit(q.u._units, spec="", registry=ur, sort_dims=False)
+        == "meter * newton"
+    )
+
+    # this prints "1 m·N", not "1 N·m" unless sort_dims is True
+    # print(q)
+
+
+@pytest.mark.xfail
+def test_issues_1841_xfail():
+    import pint
+
+    # sets compact display mode
+    ur = UnitRegistry()
+    ur.default_format = "~P"
+
+    q = ur.Quantity("2*pi radian * hour")
+
+    # Note that `radian` (and `bit` and `count`) are treated as dimensionless.
+    # And note that dimensionless quantities are stripped by this process,
+    # leading to errorneous output.  Suggestions?
+    assert (
+        pint.formatting.format_unit(q.u._units, spec="", registry=ur, sort_dims=True)
+        == "radian * hour"
+    )
+    assert (
+        pint.formatting.format_unit(q.u._units, spec="", registry=ur, sort_dims=False)
+        == "hour * radian"
+    )
+
+    # this prints "2*pi hour * radian", not "2*pi radian * hour" unless sort_dims is True
+    # print(q)

From eae68562c4663577b80fbfe50ee63e00ace7b721 Mon Sep 17 00:00:00 2001
From: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
Date: Sun, 22 Oct 2023 18:35:32 -0400
Subject: [PATCH 04/13] Documentation and code cleanups

Incorporate more code review feedback and fix some doc issues.

Signed-off-by: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
---
 docs/getting/tutorial.rst | 24 ++++++++++++++++++++++--
 pint/default_en.txt       |  1 +
 pint/formatting.py        | 33 ++++++++++++++-------------------
 3 files changed, 37 insertions(+), 21 deletions(-)

diff --git a/docs/getting/tutorial.rst b/docs/getting/tutorial.rst
index 28041339d..b98516043 100644
--- a/docs/getting/tutorial.rst
+++ b/docs/getting/tutorial.rst
@@ -91,6 +91,26 @@ a ``Quantity()`` object.
 ``Quantity()`` objects also work well with NumPy arrays, which you can
 read about in the section on :doc:`NumPy support <numpy>`.
 
+Some units are compound, such as [energy], which is stated in terms of
+[mass] * [length]**2 / [time]**2.  Earlier versions of Pint would sort unit names
+alphabetically by default, leading to different orderings of units (old behavior):
+
+    >>> "{:P}".format(pint.Quantity('1 pound * ft**2 * second**-2'))
+    '1.0 foot²·pound/second²'
+    >>> "{:P}".format(pint.Quantity('1 kg * cm**2 * second**-2'))
+    '1.0 centimeter²·kilogram/second²'
+
+Now by default it sorts by dimensions as proposed by ISO 80000, with [mass]
+coming before [length], which also comes before [time].  The dimension order
+can be changed in the registry (`dim_order` in `defaults`):
+
+    >>> "{:P}".format(pint.Quantity('1 pound * ft**2 * second**-2'))
+    '1.0 pound·foot²/second²'
+    >>> "{:P}".format(pint.Quantity('1 kg * cm**2 * second**-2'))
+    '1.0 kilogram·centimeter²/second²'
+
+
+
 Converting to different units
 -----------------------------
 
@@ -180,11 +200,11 @@ but otherwise keeping your unit definitions intact.
    >>> volume = 10*ureg.cc
    >>> mass = density*volume
    >>> print(mass)
-   14.0 cubic_centimeter * gram / centimeter ** 3
+   14.0 gram * cubic_centimeter / centimeter ** 3
    >>> print(mass.to_reduced_units())
    14.0 gram
    >>> print(mass)
-   14.0 cubic_centimeter * gram / centimeter ** 3
+   14.0 gram * cubic_centimeter / centimeter ** 3
    >>> mass.ito_reduced_units()
    >>> print(mass)
    14.0 gram
diff --git a/pint/default_en.txt b/pint/default_en.txt
index 391eeb37a..ed8e204f5 100644
--- a/pint/default_en.txt
+++ b/pint/default_en.txt
@@ -56,6 +56,7 @@
 @defaults
     group = international
     system = mks
+    # This default order for sorting dimensions was described in the proposed ISO 80000 specification.
     dim_order = [ "[substance]", "[mass]", "[current]", "[luminosity]", "[length]", "[]", "[time]", "[temperature]", ]
 @end
 
diff --git a/pint/formatting.py b/pint/formatting.py
index b158da623..9b81209a3 100644
--- a/pint/formatting.py
+++ b/pint/formatting.py
@@ -14,7 +14,6 @@
 import re
 import warnings
 from typing import Callable, Any, TYPE_CHECKING, TypeVar, List, Optional, Tuple, Union
-from collections import OrderedDict
 from collections.abc import Iterable
 from numbers import Number
 
@@ -189,6 +188,7 @@ def wrapper(func):
 
 @register_unit_format("P")
 def format_pretty(unit: UnitsContainer, registry: UnitRegistry, **options) -> str:
+    breakpoint()
     return formatter(
         unit.items(),
         as_ratio=True,
@@ -223,18 +223,15 @@ def latex_escape(string: str) -> str:
 def format_latex(unit: UnitsContainer, registry: UnitRegistry, **options) -> str:
     # Lift the sorting by dimensions b/c the preprocessed units are unrecognizeable
     sorted_units = dim_sort(unit.items(), registry)
-    preprocessed_list = [
+    preprocessed = [
         (
             rf"\mathrm{{{latex_escape(u)}}}",
             p,
         )
         for u, p in sorted_units
     ]
-    preprocessed = OrderedDict()
-    for k, v in preprocessed_list:
-        preprocessed[k] = v
     formatted = formatter(
-        preprocessed.items(),
+        preprocessed,
         as_ratio=True,
         single_denominator=True,
         product_fmt=r" \cdot ",
@@ -311,7 +308,7 @@ def format_compact(unit: UnitsContainer, registry: UnitRegistry, **options) -> s
 
 
 def dim_sort(items: Iterable[Tuple[str, Number]], registry: UnitRegistry):
-    """Sort a list of units by dimensional order.
+    """Sort a list of units by dimensional order (from `registry._defaults['dim_order']`).
 
     Parameters
     ----------
@@ -332,17 +329,16 @@ def dim_sort(items: Iterable[Tuple[str, Number]], registry: UnitRegistry):
     """
     if registry is None or len(items) <= 1:
         return items
-    # if len(items) == 2 and items[0][1] * items[1][1] < 0:
-    #     return items
     ret_dict = dict()
-    for name, value in items:
-        cname = registry.get_name(name)
+    dim_order = registry._defaults["dim_order"]
+    for unit_name, unit_exponent in items:
+        cname = registry.get_name(unit_name)
         if not cname:
             continue
         cname_dims = registry.get_dimensionality(cname)
         if len(cname_dims) == 0:
             cname_dims = {"[]": None}
-        dim_types = iter(registry._defaults["dim_order"])
+        dim_types = iter(dim_order)
         while True:
             try:
                 dim = next(dim_types)
@@ -351,20 +347,17 @@ def dim_sort(items: Iterable[Tuple[str, Number]], registry: UnitRegistry):
                         ret_dict[dim] = list()
                     ret_dict[dim].append(
                         (
-                            name,
-                            value,
+                            unit_name,
+                            unit_exponent,
                         )
                     )
                     break
             except StopIteration:
                 raise KeyError(
-                    f"Unit {name} (aka {cname}) has no recognized dimensions"
+                    f"Unit {unit_name} (aka {cname}) has no recognized dimensions"
                 )
 
-    ret = sum(
-        [ret_dict[dim] for dim in registry._defaults["dim_order"] if dim in ret_dict],
-        [],
-    )
+    ret = sum([ret_dict[dim] for dim in dim_order if dim in ret_dict], [])
     return ret
 
 
@@ -417,6 +410,8 @@ def formatter(
         True to sort the units dimentionally (Default value = False).
         When dimensions have multiple units, sort by "most significant dimension" the unit contains
         When both `sort` and `sort_dims` are True, sort alphabetically within sorted dimensions
+        ISO 80000 and other sources guide on how dimensions shoule be ordered; the user
+        can set their preference in the registry.
     registry : UnitRegistry, optional
         The registry to use if `sort_dims` is True
 

From 58f2461016ee3c071ec72602a6bb665d3a73cec0 Mon Sep 17 00:00:00 2001
From: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
Date: Sun, 22 Oct 2023 18:39:10 -0400
Subject: [PATCH 05/13] Update formatting.py

Remove `breakpoint()` left in by mistake.

Signed-off-by: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
---
 pint/formatting.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/pint/formatting.py b/pint/formatting.py
index 9b81209a3..82661f376 100644
--- a/pint/formatting.py
+++ b/pint/formatting.py
@@ -188,7 +188,6 @@ def wrapper(func):
 
 @register_unit_format("P")
 def format_pretty(unit: UnitsContainer, registry: UnitRegistry, **options) -> str:
-    breakpoint()
     return formatter(
         unit.items(),
         as_ratio=True,

From b4b461609fab62eb38471f0de664242f5eae2a21 Mon Sep 17 00:00:00 2001
From: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
Date: Sun, 22 Oct 2023 18:48:32 -0400
Subject: [PATCH 06/13] Update tutorial.rst

More attempts to make doc text and doc build happy.

Signed-off-by: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
---
 docs/getting/tutorial.rst | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/docs/getting/tutorial.rst b/docs/getting/tutorial.rst
index b98516043..0f75f5c97 100644
--- a/docs/getting/tutorial.rst
+++ b/docs/getting/tutorial.rst
@@ -95,19 +95,23 @@ Some units are compound, such as [energy], which is stated in terms of
 [mass] * [length]**2 / [time]**2.  Earlier versions of Pint would sort unit names
 alphabetically by default, leading to different orderings of units (old behavior):
 
-    >>> "{:P}".format(pint.Quantity('1 pound * ft**2 * second**-2'))
-    '1.0 foot²·pound/second²'
-    >>> "{:P}".format(pint.Quantity('1 kg * cm**2 * second**-2'))
-    '1.0 centimeter²·kilogram/second²'
+.. doctest::
+
+    >>> "{:P}".format(ureg.parse_units('pound * ft**2 * second**-2'))
+    'foot²·pound/second²'
+    >>> "{:P}".format(ureg.parse_units('kg * cm**2 * second**-2'))
+    'centimeter²·kilogram/second²'
 
 Now by default it sorts by dimensions as proposed by ISO 80000, with [mass]
 coming before [length], which also comes before [time].  The dimension order
 can be changed in the registry (`dim_order` in `defaults`):
 
-    >>> "{:P}".format(pint.Quantity('1 pound * ft**2 * second**-2'))
-    '1.0 pound·foot²/second²'
-    >>> "{:P}".format(pint.Quantity('1 kg * cm**2 * second**-2'))
-    '1.0 kilogram·centimeter²/second²'
+.. doctest::
+
+    >>> "{:P}".format(ureg.parse_units('pound * ft**2 * second**-2'))
+    'pound·foot²/second²'
+    >>> "{:P}".format(ureg.parse_units('kg * cm**2 * second**-2'))
+    'kilogram·centimeter²/second²'
 
 
 

From 45a39097fc675e564b1f235380674ebb6c35be95 Mon Sep 17 00:00:00 2001
From: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
Date: Sun, 22 Oct 2023 18:59:03 -0400
Subject: [PATCH 07/13] Update tutorial.rst

See whether I've turned off doctest where old behavior is no longer easily reproducible.

Signed-off-by: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
---
 docs/getting/tutorial.rst | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/docs/getting/tutorial.rst b/docs/getting/tutorial.rst
index 0f75f5c97..e3c25fe44 100644
--- a/docs/getting/tutorial.rst
+++ b/docs/getting/tutorial.rst
@@ -95,12 +95,12 @@ Some units are compound, such as [energy], which is stated in terms of
 [mass] * [length]**2 / [time]**2.  Earlier versions of Pint would sort unit names
 alphabetically by default, leading to different orderings of units (old behavior):
 
-.. doctest::
-
+```ignore
     >>> "{:P}".format(ureg.parse_units('pound * ft**2 * second**-2'))
     'foot²·pound/second²'
     >>> "{:P}".format(ureg.parse_units('kg * cm**2 * second**-2'))
     'centimeter²·kilogram/second²'
+```
 
 Now by default it sorts by dimensions as proposed by ISO 80000, with [mass]
 coming before [length], which also comes before [time].  The dimension order

From 69f947493c3ebdd261110275bcf1e042bf4627c6 Mon Sep 17 00:00:00 2001
From: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
Date: Sun, 22 Oct 2023 19:02:31 -0400
Subject: [PATCH 08/13] Update tutorial.rst

And another attempt.

Signed-off-by: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
---
 docs/getting/tutorial.rst | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/docs/getting/tutorial.rst b/docs/getting/tutorial.rst
index e3c25fe44..d0b9347bf 100644
--- a/docs/getting/tutorial.rst
+++ b/docs/getting/tutorial.rst
@@ -95,10 +95,10 @@ Some units are compound, such as [energy], which is stated in terms of
 [mass] * [length]**2 / [time]**2.  Earlier versions of Pint would sort unit names
 alphabetically by default, leading to different orderings of units (old behavior):
 
-```ignore
-    >>> "{:P}".format(ureg.parse_units('pound * ft**2 * second**-2'))
+```
+    "{:P}".format(ureg.parse_units('pound * ft**2 * second**-2')) would yield:
     'foot²·pound/second²'
-    >>> "{:P}".format(ureg.parse_units('kg * cm**2 * second**-2'))
+    "{:P}".format(ureg.parse_units('kg * cm**2 * second**-2')) would yield:
     'centimeter²·kilogram/second²'
 ```
 

From 271197096bc8f29216e598830471f9c15efcb4eb Mon Sep 17 00:00:00 2001
From: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
Date: Thu, 11 Jan 2024 14:35:19 +1300
Subject: [PATCH 09/13] Update __init__.py

Prepare to merge `develop` into this PR.

Signed-off-by: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
---
 pint/delegates/formatter/__init__.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/pint/delegates/formatter/__init__.py b/pint/delegates/formatter/__init__.py
index c30f3657b..55b44b31e 100644
--- a/pint/delegates/formatter/__init__.py
+++ b/pint/delegates/formatter/__init__.py
@@ -8,9 +8,10 @@
 
 
 from .base_formatter import BaseFormatter
+from .iso80000_formatter import ISO80000Formatter
 
 
-class Formatter(BaseFormatter):
+class Formatter(ISO80000Formatter, BaseFormatter):
     # TODO: this should derive from all relevant formaters to
     # reproduce the current behavior of Pint.
     pass

From f9e9dbad74cf7a8da00c064ec639397f19f0ed2c Mon Sep 17 00:00:00 2001
From: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
Date: Mon, 15 Jan 2024 17:28:09 +1300
Subject: [PATCH 10/13] Add dim_order to BaseFormatter

Move the proposed `dim_sort` functionality from being a system registry property to being a formatter property, specifically `BaseFormatter`.

Also fix typos noticed in `pint/testsuite/conftest.py`.

Signed-off-by: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
---
 CHANGES                                    | 2 +-
 pint/default_en.txt                        | 2 --
 pint/delegates/formatter/__init__.py       | 5 ++---
 pint/delegates/formatter/base_formatter.py | 3 +++
 pint/facets/plain/definitions.py           | 5 +----
 pint/formatting.py                         | 4 ++--
 pint/testsuite/conftest.py                 | 6 +++---
 7 files changed, 12 insertions(+), 15 deletions(-)

diff --git a/CHANGES b/CHANGES
index 01f5644c0..2b0754435 100644
--- a/CHANGES
+++ b/CHANGES
@@ -4,9 +4,9 @@ Pint Changelog
 0.24 (unreleased)
 -----------------
 
+- Add `dim_order` property to BaseFormatter.
 - Add `dim_sort` parameter to formatter.
   (PR #1864, fixes Issue #1841)
-- Nothing changed yet.
 
 
 0.23 (2023-12-08)
diff --git a/pint/default_en.txt b/pint/default_en.txt
index ed8e204f5..5fc7f8265 100644
--- a/pint/default_en.txt
+++ b/pint/default_en.txt
@@ -56,8 +56,6 @@
 @defaults
     group = international
     system = mks
-    # This default order for sorting dimensions was described in the proposed ISO 80000 specification.
-    dim_order = [ "[substance]", "[mass]", "[current]", "[luminosity]", "[length]", "[]", "[time]", "[temperature]", ]
 @end
 
 
diff --git a/pint/delegates/formatter/__init__.py b/pint/delegates/formatter/__init__.py
index 707abc677..814156afb 100644
--- a/pint/delegates/formatter/__init__.py
+++ b/pint/delegates/formatter/__init__.py
@@ -7,11 +7,10 @@
 """
 
 
-from .base_formatter import BabelFormatter
-from .iso80000_formatter import ISO80000Formatter
+from .base_formatter import BaseFormatter, BabelFormatter
 
 
-class Formatter(ISO80000Formatter, BabelFormatter):
+class Formatter(BabelFormatter, BaseFormatter):
     # TODO: this should derive from all relevant formaters to
     # reproduce the current behavior of Pint.
     pass
diff --git a/pint/delegates/formatter/base_formatter.py b/pint/delegates/formatter/base_formatter.py
index d15a7a6a6..d618b2140 100644
--- a/pint/delegates/formatter/base_formatter.py
+++ b/pint/delegates/formatter/base_formatter.py
@@ -34,6 +34,9 @@
 
 
 class BaseFormatter:
+    # This default order for sorting dimensions was described in the proposed ISO 80000 specification.
+    dim_order = ( "[substance]", "[mass]", "[current]", "[luminosity]", "[length]", "[]", "[time]", "[temperature]", )
+
     def format_quantity(
         self, quantity: PlainQuantity[MagnitudeT], spec: str = ""
     ) -> str:
diff --git a/pint/facets/plain/definitions.py b/pint/facets/plain/definitions.py
index 05cb055a0..c32637e75 100644
--- a/pint/facets/plain/definitions.py
+++ b/pint/facets/plain/definitions.py
@@ -14,7 +14,7 @@
 import ast
 from dataclasses import dataclass
 from functools import cached_property
-from typing import Any, List, Optional
+from typing import Any, Optional
 
 from ..._typing import Magnitude
 from ... import errors
@@ -61,15 +61,12 @@ class DefaultsDefinition:
 
     group: ty.Optional[str]
     system: ty.Optional[str]
-    dim_order: ty.Optional[List[str]]
 
     def items(self):
         if self.group is not None:
             yield "group", self.group
         if self.system is not None:
             yield "system", self.system
-        if self.dim_order is not None:
-            yield "dim_order", ast.literal_eval(self.dim_order)
 
 
 @dataclass(frozen=True)
diff --git a/pint/formatting.py b/pint/formatting.py
index 82661f376..57846a88d 100644
--- a/pint/formatting.py
+++ b/pint/formatting.py
@@ -307,7 +307,7 @@ def format_compact(unit: UnitsContainer, registry: UnitRegistry, **options) -> s
 
 
 def dim_sort(items: Iterable[Tuple[str, Number]], registry: UnitRegistry):
-    """Sort a list of units by dimensional order (from `registry._defaults['dim_order']`).
+    """Sort a list of units by dimensional order (from `registry.formatter.dim_order`).
 
     Parameters
     ----------
@@ -329,7 +329,7 @@ def dim_sort(items: Iterable[Tuple[str, Number]], registry: UnitRegistry):
     if registry is None or len(items) <= 1:
         return items
     ret_dict = dict()
-    dim_order = registry._defaults["dim_order"]
+    dim_order = registry.formatter.dim_order
     for unit_name, unit_exponent in items:
         cname = registry.get_name(unit_name)
         if not cname:
diff --git a/pint/testsuite/conftest.py b/pint/testsuite/conftest.py
index d51bc8c05..201e56a0e 100644
--- a/pint/testsuite/conftest.py
+++ b/pint/testsuite/conftest.py
@@ -70,19 +70,19 @@ def func_registry():
 
 @pytest.fixture(scope="class")
 def class_registry():
-    """Only use for those test that do not modify the registry."""
+    """Only use for those tests that do not modify the registry."""
     return pint.UnitRegistry()
 
 
 @pytest.fixture(scope="module")
 def module_registry():
-    """Only use for those test that do not modify the registry."""
+    """Only use for those tests that do not modify the registry."""
     return pint.UnitRegistry()
 
 
 @pytest.fixture(scope="session")
 def sess_registry():
-    """Only use for those test that do not modify the registry."""
+    """Only use for those tests that do not modify the registry."""
     return pint.UnitRegistry()
 
 

From 0b049656a59788202c3ed4236eddbbc5ad6b783e Mon Sep 17 00:00:00 2001
From: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
Date: Mon, 15 Jan 2024 17:33:07 +1300
Subject: [PATCH 11/13] Make black and ruff happy.

Signed-off-by: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
---
 pint/delegates/formatter/base_formatter.py | 11 ++++++++++-
 pint/facets/plain/definitions.py           |  1 -
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/pint/delegates/formatter/base_formatter.py b/pint/delegates/formatter/base_formatter.py
index d618b2140..f0db6c5ff 100644
--- a/pint/delegates/formatter/base_formatter.py
+++ b/pint/delegates/formatter/base_formatter.py
@@ -35,7 +35,16 @@
 
 class BaseFormatter:
     # This default order for sorting dimensions was described in the proposed ISO 80000 specification.
-    dim_order = ( "[substance]", "[mass]", "[current]", "[luminosity]", "[length]", "[]", "[time]", "[temperature]", )
+    dim_order = (
+        "[substance]",
+        "[mass]",
+        "[current]",
+        "[luminosity]",
+        "[length]",
+        "[]",
+        "[time]",
+        "[temperature]",
+    )
 
     def format_quantity(
         self, quantity: PlainQuantity[MagnitudeT], spec: str = ""
diff --git a/pint/facets/plain/definitions.py b/pint/facets/plain/definitions.py
index c32637e75..44bf29858 100644
--- a/pint/facets/plain/definitions.py
+++ b/pint/facets/plain/definitions.py
@@ -11,7 +11,6 @@
 import itertools
 import numbers
 import typing as ty
-import ast
 from dataclasses import dataclass
 from functools import cached_property
 from typing import Any, Optional

From 41dcc421108fab67a1c41a6578fe242b516dbeaa Mon Sep 17 00:00:00 2001
From: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
Date: Mon, 15 Jan 2024 17:38:28 +1300
Subject: [PATCH 12/13] Update requirements_docs.txt

Based on this error message from the CI build:

```
Run sphinx-build -n -j auto -b html -d build/doctrees docs build/html
  sphinx-build -n -j auto -b html -d build/doctrees docs build/html
  shell: /usr/bin/bash -e {0}
  env:
    pythonLocation: /opt/hostedtoolcache/Python/3.9.18/x64
    LD_LIBRARY_PATH: /opt/hostedtoolcache/Python/3.9.18/x64/lib
Running Sphinx v4.5.0

Sphinx version error:
The sphinxcontrib.applehelp extension used by this project needs at least Sphinx v5.0; it therefore cannot be built with this version.
Error: Process completed with exit code 2.
```

bump sphinx to >= 5 (>4 only got us to 4.5).

Signed-off-by: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
---
 requirements_docs.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/requirements_docs.txt b/requirements_docs.txt
index 8f4410960..68a96efb1 100644
--- a/requirements_docs.txt
+++ b/requirements_docs.txt
@@ -1,4 +1,4 @@
-sphinx>4
+sphinx>=5
 ipython<=8.12
 matplotlib
 mip>=1.13

From 957e9ca61d6e2e5f3217728ede059234ee9c3b30 Mon Sep 17 00:00:00 2001
From: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>
Date: Mon, 15 Jan 2024 17:40:41 +1300
Subject: [PATCH 13/13] Revert "Update requirements_docs.txt"

This reverts commit 41dcc421108fab67a1c41a6578fe242b516dbeaa.
---
 requirements_docs.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/requirements_docs.txt b/requirements_docs.txt
index 68a96efb1..8f4410960 100644
--- a/requirements_docs.txt
+++ b/requirements_docs.txt
@@ -1,4 +1,4 @@
-sphinx>=5
+sphinx>4
 ipython<=8.12
 matplotlib
 mip>=1.13