Clean and export the units registry

src/xclim/core/dataflags.py

@@ -8,7 +8,6 @@
 from __future__ import annotations
 
 from collections.abc import Callable, Sequence
-from decimal import Decimal
 from functools import reduce
 from inspect import signature
 
@@ -674,7 +673,7 @@ def _get_variable_name(function, _kwargs):
                     format_args[arg] = "array"
                 else:
                     val = str2pint(val).magnitude
-                    if Decimal(val) % 1 == 0:
+                    if val == int(val):
                         val = str(int(val))
                     else:
                         val = str(val).replace(".", "point")

src/xclim/core/indicator.py

@@ -1311,7 +1311,7 @@ def _format(
         # Add formatting {} around values to be able to replace them with _attrs_mapping using format.
         for k, v in args.items():
             if isinstance(v, units.Quantity):
-                mba[k] = f"{v:g~P}"
+                mba[k] = f"{v:gcf}"
             elif isinstance(v, int | float):
                 mba[k] = f"{v:g}"
             # TODO: What about InputKind.NUMBER_SEQUENCE

src/xclim/core/units.py

@@ -22,7 +22,6 @@
 import pint
 import xarray as xr
 from boltons.funcutils import wraps
-from pint import UndefinedUnitError
 from yaml import safe_load
 
 from xclim.core._exceptions import ValidationError
@@ -64,28 +63,21 @@
 units = deepcopy(cf_xarray.units.units)
 # Changing the default string format for units/quantities.
 # CF is implemented by cf-xarray, g is the most versatile float format.
-# The following try/except logic can be removed when xclim drops support numpy <2.0.
-try:
-    units.formatter.default_format = "gcf"
-except UndefinedUnitError:
-    units.default_format = "gcf"
-# Switch this flag back to False. Not sure what that implies, but it breaks some tests.
-units.force_ndarray_like = False  # noqa: F841
-# Another alias not included by cf_xarray
-units.define("@alias percent = pct")
-
-# Default context.
-null = pint.Context("none")
-units.add_context(null)
+units.formatter.default_format = "gcf"
+# CF-xarray forces numpy arrays even for scalar values, not sure why.
+# We don't want that in xclim, the magnitude of a scalar is a scalar (float).
+units.force_ndarray_like = False
 
-# Precipitation units. This is an artificial unit that we're using to verify that a given unit can be converted into
-# a precipitation unit. Ideally this could be checked through the `dimensionality`, but I can't get it to work.
+# Define dimensionalities for convenience with the `declare_units` decorator
 units.define("[precipitation] = [mass] / [length] ** 2 / [time]")
-units.define("mmday = 1 kg / meter ** 2 / day")
-
 units.define("[discharge] = [length] ** 3 / [time]")
-units.define("cms = meter ** 3 / second")
+units.define("[radiation] = [power] / [length]**2")
 
+# Default context. This is essentially a convenience, so that we can pass a context systemtically to pint's methods.
+null = pint.Context("none")
+units.add_context(null)
+
+# Convenience context for common transformation involving liquid water
 hydro = pint.Context("hydro")
 hydro.add_transformation(
     "[mass] / [length]**2",
@@ -109,6 +101,9 @@
 )
 units.add_context(hydro)
 
+# Set as application registry
+pint.set_application_registry(units)
+
 
 with (files("xclim.data") / "variables.yml").open() as variables:
     CF_CONVERSIONS = safe_load(variables)["conversions"]
@@ -136,10 +131,6 @@ def _func_register(func: Callable) -> Callable:
     return _func_register
 
 
-# Radiation units
-units.define("[radiation] = [power] / [length]**2")
-
-
 def units2pint(
     value: xr.DataArray | units.Unit | units.Quantity | dict | str,
 ) -> pint.Unit:

src/xclim/indices/_threshold.py

@@ -2963,7 +2963,7 @@ def maximum_consecutive_tx_days(
 
 @declare_units(siconc="[]", areacello="[area]", thresh="[]")
 def sea_ice_area(
-    siconc: xarray.DataArray, areacello: xarray.DataArray, thresh: Quantified = "15 pct"
+    siconc: xarray.DataArray, areacello: xarray.DataArray, thresh: Quantified = "15 %"
 ) -> xarray.DataArray:
     """
     Total sea ice area.
@@ -2994,15 +2994,15 @@ def sea_ice_area(
     "What is the difference between sea ice area and extent?" - :cite:cts:`nsidc_frequently_2008`
     """
     t = convert_units_to(thresh, siconc)
-    factor = convert_units_to("100 pct", siconc)
+    factor = convert_units_to("100 %", siconc)
     sia = xarray.dot(siconc.where(siconc >= t, 0), areacello) / factor
     sia = sia.assign_attrs(units=areacello.units)
     return sia
 
 
 @declare_units(siconc="[]", areacello="[area]", thresh="[]")
 def sea_ice_extent(
-    siconc: xarray.DataArray, areacello: xarray.DataArray, thresh: Quantified = "15 pct"
+    siconc: xarray.DataArray, areacello: xarray.DataArray, thresh: Quantified = "15 %"
 ) -> xarray.DataArray:
     """
     Total sea ice extent.

src/xclim/indices/fire/_cffwis.py

@@ -1397,7 +1397,7 @@ def cffwis_indices(
     tas = convert_units_to(tas, "C")
     pr = convert_units_to(pr, "mm/day")
     sfcWind = convert_units_to(sfcWind, "km/h")
-    hurs = convert_units_to(hurs, "pct")
+    hurs = convert_units_to(hurs, "%")
     if snd is not None:
         snd = convert_units_to(snd, "m")
 

src/xclim/indices/fire/_ffdi.py

@@ -394,7 +394,7 @@ def mcarthur_forest_fire_danger_index(
     :cite:cts:`ffdi-noble_1980,ffdi-dowdy_2018,ffdi-holgate_2017`
     """
     tasmax = convert_units_to(tasmax, "C")
-    hurs = convert_units_to(hurs, "pct")
+    hurs = convert_units_to(hurs, "%")
     sfcWind = convert_units_to(sfcWind, "km/h")
 
     ffdi = drought_factor**0.987 * np.exp(

tests/test_indicators.py

@@ -564,18 +564,18 @@ def test_formatting(pr_series):
     # pint 0.10 now pretty print day as d.
     assert (
         out.attrs["long_name"]
-        == "Number of days with daily precipitation at or above 1 mm/d"
+        == "Number of days with daily precipitation at or above 1 mm d-1"
     )
     assert out.attrs["description"] in [
-        "Annual number of days with daily precipitation at or above 1 mm/d."
+        "Annual number of days with daily precipitation at or above 1 mm d-1."
     ]
     out = atmos.wetdays(pr_series(np.arange(366)), thresh=1.5 * units.mm / units.day)
     assert (
         out.attrs["long_name"]
-        == "Number of days with daily precipitation at or above 1.5 mm/d"
+        == "Number of days with daily precipitation at or above 1.5 mm d-1"
     )
     assert out.attrs["description"] in [
-        "Annual number of days with daily precipitation at or above 1.5 mm/d."
+        "Annual number of days with daily precipitation at or above 1.5 mm d-1."
     ]
 
 

tests/test_indices.py

@@ -3332,19 +3332,19 @@ def test_simple(self):
             np.arange(4).reshape(1, 2, 2),
             dims=["time", "lat", "lon"],
             coords={"time": [1], "lat": [-45, 45], "lon": [30, 60]},
-            attrs={"units": "mmday"},
+            attrs={"units": "mm/day"},
         )
         tas_baseline = xr.DataArray(
             np.arange(4).reshape(1, 2, 2),
             dims=["time", "lat", "lon"],
             coords={"time": [1], "lat": [-45, 45], "lon": [30, 60]},
-            attrs={"units": "C"},
+            attrs={"units": "degC"},
         )
         tas_future = xr.DataArray(
             np.arange(40).reshape(10, 2, 2),
             dims=["time_fut", "lat", "lon"],
             coords={"time_fut": np.arange(10), "lat": [-45, 45], "lon": [30, 60]},
-            attrs={"units": "C"},
+            attrs={"units": "degC"},
         )
         delta_tas = tas_future - tas_baseline
         delta_tas.attrs["units"] = "delta_degC"

tests/test_units.py

@@ -43,7 +43,6 @@ def test_hydro(self):
         with units.context("hydro"):
             q = 1 * units.kg / units.m**2 / units.s
             assert q.to("mm/day") == q.to("mm/d")
-            assert q.to("mmday").magnitude == 24 * 60**2
 
     def test_lat_lon(self):
         assert 100 * units.degreeN == 100 * units.degree
@@ -55,19 +54,15 @@ def test_pcic(self):
             np.isclose(1 * fu, 1 * tu)
 
     def test_dimensionality(self):
+        # Check that the hydro context allows flux to rate conversion
         with units.context("hydro"):
             fu = 1 * units.parse_units("kg / m**2 / s")
-            tu = 1 * units.parse_units("mm / d")
-            fu.to("mmday")
-            tu.to("mmday")
+            fu.to("mm/day")
 
     def test_fraction(self):
         q = 5 * units.percent
         assert q.to("dimensionless") == 0.05
 
-        q = 5 * units.parse_units("pct")
-        assert q.to("dimensionless") == 0.05
-
 
 class TestConvertUnitsTo:
     def test_deprecation(self, tas_series):
@@ -135,9 +130,6 @@ def test_pint2cfunits(self):
         u = units("percent")
         assert pint2cfunits(u.units) == "%"
 
-        u = units("pct")
-        assert pint2cfunits(u.units) == "%"
-
     def test_units2pint(self, pr_series):
         u = units2pint(pr_series([1, 2]))
         assert pint2cfunits(u) == "kg m-2 s-1"
@@ -168,11 +160,9 @@ def test_str2pint(self):
 class TestCheckUnits:
     def test_basic(self):
         check_units("%", "[]")
-        check_units("pct", "[]")
         check_units("mm/day", "[precipitation]")
         check_units("mm/s", "[precipitation]")
         check_units("kg/m2/s", "[precipitation]")
-        check_units("cms", "[discharge]")
         check_units("m3/s", "[discharge]")
         check_units("m/s", "[speed]")
         check_units("km/h", "[speed]")