style: fix some warnings

unfccc_di_api/unfccc_di_api.py

@@ -299,11 +299,11 @@ def __init__(
 
         try:
             parties_raw = self._get(f"parties/{party_category}")
-        except requests.JSONDecodeError:
+        except requests.JSONDecodeError as e:
             raise RuntimeError(
                 "Access to the UNFCCC API denied - see"
                 " https://github.com/pik-primap/unfccc_di_api#warning for solutions"
-            )
+            ) from e
         parties_entries = []
         for entry in parties_raw:
             if entry["categoryCode"] == party_category and entry["name"] != "Groups":
@@ -469,7 +469,7 @@ def query(
                     "try `UNFCCCSingleCategoryApiReader.parties` for a list of"
                     " valid codes"
                 )
-                raise ValueError(f"Unknown party `{code}`, {help}!")
+                raise ValueError(f"Unknown party `{code}`, {help}!") from None
 
         # always query all years
         year_ids = list(self.years.index)
@@ -584,9 +584,8 @@ def _parse_raw_answer(
                 data.append(row)
 
         df = pd.DataFrame(data)
-        df.sort_values(
+        df = df.sort_values(
             ["party", "category", "classification", "measure", "gas", "unit", "year"],
-            inplace=True,
         )
         df.drop_duplicates(inplace=True)
         df.reset_index(inplace=True, drop=True)
@@ -659,7 +658,7 @@ def _name_id(df, name: str, key: str = "name") -> int:
         try:
             return int(df[df[key] == name].index[0])
         except IndexError:
-            raise KeyError(name)
+            raise KeyError(name) from None
 
     def show_category_hierarchy(self) -> None:
         """Print the hierarchy of categories and their IDs."""