Address FutureWarnings from pandas 2.1.0

genno/core/attrseries.py

@@ -186,7 +186,7 @@ def bfill(self, dim: Hashable, limit: Optional[int] = None):
         #      if needed use _maybe_groupby()
         return self._replace(
             self.unstack(dim)
-            .fillna(method="bfill", axis=1, limit=limit)
+            .bfill(axis=1, limit=limit)
             .stack()
             .reorder_levels(self.dims),
         )
@@ -271,7 +271,7 @@ def ffill(self, dim: Hashable, limit: Optional[int] = None):
         #      if needed use _maybe_groupby()
         return self._replace(
             self.unstack(dim)
-            .fillna(method="ffill", axis=1, limit=limit)
+            .ffill(axis=1, limit=limit)
             .stack()
             .reorder_levels(self.dims),
         )

genno/tests/compat/test_pyam.py

@@ -14,6 +14,11 @@
 # Skip this entire file if pyam is not installed
 pyam = pytest.importorskip("pyam", reason="pyam-iamc not installed")
 
+# Warning emitted by pandas ≥ 2.1.0 with pyam 1.9.0
+pytestmark = pytest.mark.filterwarnings(
+    "ignore:.*unique with argument that is not.*:FutureWarning:pyam.core"
+)
+
 
 @pytest.fixture(scope="session")
 def scenario():

genno/util.py

@@ -3,6 +3,7 @@
 from inspect import Parameter, signature
 from typing import Callable, Iterable, Mapping, MutableMapping, Tuple, Type, Union
 
+import numpy as np
 import pandas as pd
 import pint
 from dask.core import literal
@@ -95,6 +96,12 @@ def parse_units(data: Iterable, registry=None) -> pint.Unit:
     """
     registry = registry or pint.get_application_registry()
 
+    # Ensure a type that is accepted by pd.unique()
+    if isinstance(data, str):
+        data = np.array([data])
+    elif not isinstance(data, (np.ndarray, pd.Index, pd.Series)):
+        data = np.array(data)
+
     unit = pd.unique(data)
 
     if len(unit) > 1: