Replaces cf-units with pint

Author: JamesVarndell

pyproject.toml

@@ -26,7 +26,7 @@ dependencies = [
   "earthkit-data",
   "earthkit-plots-default-styles",
   "cartopy>=0.22.0",
-  "cf-units",
+  "pint",
   "matplotlib",
   "pyyaml",
   "numpy",
@@ -40,9 +40,6 @@ license = {text = "Apache License Version 2.0"}
 name = "earthkit-plots"
 readme = "README.md"
 requires-python = ">=3.8"
-optional-dependencies.all = [
-  "cf_units"
-]
 optional-dependencies.test = [
   "nbconvert",
   "nbformat",

src/earthkit/plots/metadata/units.py

@@ -12,24 +12,30 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import re
+
+from pint import UnitRegistry
+
+ureg = UnitRegistry()
+Q_ = ureg.Quantity
+
+
+def _pintify(unit_str):
+    # Replace spaces with dots
+    unit_str = unit_str.replace(" ", ".")
+
+    # Insert ^ between characters and numbers (including negative numbers)
+    unit_str = re.sub(r"([a-zA-Z])(-?\d+)", r"\1^\2", unit_str)
+
+    return ureg(unit_str).units
 
-_NO_CF_UNITS = False
-try:
-    import cf_units
-except ImportError:
-    _NO_CF_UNITS = True
 
 #: Units for temperature anomalies.
 TEMPERATURE_ANOM_UNITS = [
     "kelvin",
     "celsius",
 ]
 
-#: Pretty units for temperature.
-PRETTY_UNITS = {
-    "celsius": "°C",
-    "fahrenheit": "°F",
-}
 
 #: Unit equivalences.
 UNIT_EQUIVALENCE = {
@@ -48,9 +54,7 @@ def are_equal(unit_1, unit_2):
     unit_2 : str
         The second unit.
     """
-    if _NO_CF_UNITS:
-        raise ImportError("cf-units is required for checking unit equivalence")
-    return cf_units.Unit(unit_1) == cf_units.Unit(unit_2)
+    return _pintify(unit_1) == _pintify(unit_2)
 
 
 def anomaly_equivalence(units):
@@ -81,24 +85,24 @@ def convert(data, source_units, target_units):
     target_units : str
         The units to convert to.
     """
-    if _NO_CF_UNITS:
-        raise ImportError("cf-units is required for unit conversion")
+    source_units = _pintify(source_units)
+    target_units = _pintify(target_units)
     try:
-        result = cf_units.Unit(source_units).convert(data, target_units)
+        result = (data * source_units).to(target_units).magnitude
     except ValueError as err:
         for units in UNIT_EQUIVALENCE:
-            if cf_units.Unit(source_units) == cf_units.Unit(units):
+            if source_units == _pintify(units):
                 try:
-                    equal_units = UNIT_EQUIVALENCE[units]
-                    result = cf_units.Unit(equal_units).convert(data, target_units)
+                    equal_units = _pintify(UNIT_EQUIVALENCE[units])
+                    result = (data * equal_units).to(target_units)
                 except ValueError:
                     raise err
                 else:
                     break
     return result
 
 
-def format_units(units):
+def format_units(units, exponential_notation=False):
     """
     Format units for display in LaTeX.
 
@@ -112,27 +116,7 @@ def format_units(units):
     >>> format_units("kg m-2")
     "$kg m^{-2}$"
     """
-    if _NO_CF_UNITS:
-        return f"${PRETTY_UNITS.get(units, units)}$"
-
-    from cf_units.tex import tex
-
-    for name, formatted_units in PRETTY_UNITS.items():
-        try:
-            if are_equal(units, name):
-                units = formatted_units
-                break
-        except ValueError:
-            continue
-    else:
-        try:
-            units = str(cf_units.Unit(units))
-        except ValueError:
-            pass
-
-    try:
-        formatted_units = f"${tex(units)}$"
-    except SyntaxError:
-        formatted_units = units
-
-    return formatted_units
+    latex_str = f"{_pintify(units):~L}"
+    if exponential_notation:
+        raise NotImplementedError("Exponential notation is not yet supported.")
+    return f"${latex_str}$"

src/earthkit/plots/styles/__init__.py

@@ -13,7 +13,6 @@
 # limitations under the License.
 
 import inspect
-import warnings
 
 import matplotlib as mpl
 import matplotlib.pyplot as plt
@@ -82,7 +81,6 @@ class Style:
         any data incompatible with these units will not be able to use this
         `Style`. If `units` are not provided, then data plotted using this
         `Style` will remain in their original units.
-        Note that passing `units` requires `cf_units` to be installed.
     units_label : str, optional
         The label to use in titles and legends to represent the units of the
         data.
@@ -128,13 +126,6 @@ def __init__(
         self.normalize = normalize
         self.gradients = gradients
 
-        if units is not None and metadata.units._NO_CF_UNITS:
-            warnings.warn(
-                "You must have cf-units installed to use unit conversion "
-                "features; since no cf-units installation was found, no units "
-                "will be applied to this style"
-            )
-            units = None
         self._units = units
         self._units_label = units_label
         self.scale_factor = scale_factor
@@ -219,7 +210,7 @@ def convert_units(self, values, source_units, short_name=""):
         values : numpy.ndarray
             The values to convert from their source units to this `Style`'s
             units.
-        source_units : str or cf_units.Unit
+        source_units : str
             The source units of the given values.
         short_name : str, optional
             The short name of the variable, which is used to make extra

src/earthkit/plots/styles/auto.py

@@ -20,7 +20,7 @@
 
 from earthkit.plots import styles
 from earthkit.plots._plugins import PLUGINS
-from earthkit.plots.metadata.units import _NO_CF_UNITS, are_equal
+from earthkit.plots.metadata.units import are_equal
 from earthkit.plots.schemas import schema
 
 
@@ -42,7 +42,7 @@ def guess_style(data, units=None, **kwargs):
         data, the data will be converted to the target units and the style
         will be adjusted accordingly.
     """
-    if not schema.automatic_styles or schema.style_library is None or _NO_CF_UNITS:
+    if not schema.automatic_styles or schema.style_library is None:
         return styles.DEFAULT_STYLE
 
     if schema.style_library not in PLUGINS: