Adapt to current pint

HISTORY.rst

@@ -35,6 +35,7 @@ Bug fixes
 ^^^^^^^^^
 * The docstring of ``cool_night_index`` suggested that `lat` was an optional parameter. This has been corrected. (:issue:`1179`, :pull:`1180`).
 * The ``mean_radiant_temperature`` indice was accessing hardcoded `lat` and `lon` coordinates from passed DataArrays. This now uses `cf-xarray` accessors. (:pull:`1180`).
+* Adopt (and adapt) unit registry declaration and preprocessors from ``cf-xarray`` to circumvent bugs caused by a refactor in ``pint`` 0.20. It also cleans the code a little bit. (:issue:`1211`, :pull:`1212`).
 
 Internal changes
 ^^^^^^^^^^^^^^^^

xclim/core/units.py

@@ -8,17 +8,15 @@
 """
 from __future__ import annotations
 
+import functools
 import re
 import warnings
 from inspect import signature
 from typing import Any, Callable
 
-import pint.converters
-import pint.unit
+import pint
 import xarray as xr
 from boltons.funcutils import wraps
-from pint import Unit
-from pint.definitions import UnitDefinition
 
 from .calendar import date_range, get_calendar, parse_offset
 from .options import datacheck
@@ -41,12 +39,22 @@
 ]
 
 
-units = pint.UnitRegistry(autoconvert_offset_to_baseunit=True, on_redefinition="ignore")
-units.define(
-    pint.unit.UnitDefinition(
-        "percent", "%", ("pct",), pint.converters.ScaleConverter(0.01)
-    )
+# shamelessly adapted from `cf-xarray` (which adopted it from MetPy and xclim itself)
+units = pint.UnitRegistry(
+    autoconvert_offset_to_baseunit=True,
+    preprocessors=[
+        functools.partial(
+            re.compile(
+                r"(?<=[A-Za-z])(?![A-Za-z])(?<![0-9\-][eE])(?<![0-9\-])(?=[0-9\-])"
+            ).sub,
+            "**",
+        ),
+        lambda string: string.replace("%", "percent"),
+    ],
 )
+
+units.define("percent = 0.01 = % = pct")
+
 # In pint, the default symbol for year is "a" which is not CF-compliant (stands for "are")
 units.define("year = 365.25 * day = yr")
 
@@ -110,7 +118,7 @@
 units.define("[radiation] = [power] / [length]**2")
 
 
-def units2pint(value: xr.DataArray | str | units.Quantity) -> Unit:
+def units2pint(value: xr.DataArray | str | units.Quantity) -> pint.Unit:
     """Return the pint Unit for the DataArray units.
 
     Parameters
@@ -120,17 +128,9 @@ def units2pint(value: xr.DataArray | str | units.Quantity) -> Unit:
 
     Returns
     -------
-    pint.unit.UnitDefinition
+    pint.Unit
         Units of the data array.
     """
-
-    def _transform(s):
-        """Convert a CF-unit string to a pint expression."""
-        if s == "%":
-            return "percent"
-
-        return re.subn(r"([a-zA-Z]+)\^?(-?\d)", r"\g<1>**\g<2>", s)[0]
-
     if isinstance(value, str):
         unit = value
     elif isinstance(value, xr.DataArray):
@@ -163,19 +163,11 @@ def _transform(s):
             "Remove white space from temperature units, e.g. use `degC`."
         )
 
-    try:  # Pint compatible
-        return units.parse_units(unit)
-    except (
-        pint.UndefinedUnitError,
-        pint.DimensionalityError,
-        AttributeError,
-        TypeError,
-    ):  # Convert from CF-units to pint-compatible
-        return units.parse_units(_transform(unit))
+    return units.parse_units(unit)
 
 
 # Note: The pint library does not have a generic Unit or Quantity type at the moment. Using "Any" as a stand-in.
-def pint2cfunits(value: UnitDefinition) -> str:
+def pint2cfunits(value: pint.Unit) -> str:
     """Return a CF-compliant unit string from a `pint` unit.
 
     Parameters
@@ -210,7 +202,8 @@ def repl(m):
     out = out.replace(" * ", " ")
     # Delta degrees:
     out = out.replace("Δ°", "delta_deg")
-    return out.replace("percent", "%")
+    # Percents
+    return out.replace("percent", "%").replace("pct", "%")
 
 
 def ensure_cf_units(ustr: str) -> str: