Small cleanups: idiomatic Python and a precedence fix

- waterdata/utils.py: replace runtime `assert` in `_check_ogc_requests`
  with an explicit `ValueError` (assertions can be disabled with `-O`).
- waterdata/utils.py: fix operator-precedence bug in `_format_datetime`
  where `len==1 and re.search(...) or "/" in datetime_input[0]` would
  short-circuit and return `datetime_input[0]` for 2-element inputs
  whose first element contained "/". Parenthesize so both branches
  require `len==1`.
- nwis.py: `"dec_lat_va" in list(df)` -> `in df.columns` (drop needless
  list construction).
- nwis.py: replace index-based `for i in range(len(index_list)-1)` loop
  with `zip(index_list[:-1], index_list[1:])`.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: thodson-usgs

dataretrieval/nwis.py

@@ -96,7 +96,7 @@ def format_response(
     if service == "peaks":
         df = preformat_peaks_response(df)
 
-    if gpd is not None and "dec_lat_va" in list(df):
+    if gpd is not None and "dec_lat_va" in df.columns:
         geoms = gpd.points_from_xy(df.dec_long_va.values, df.dec_lat_va.values)
         df = gpd.GeoDataFrame(df, geometry=geoms, crs=_CRS)
 
@@ -993,9 +993,7 @@ def _read_json(json):
     )
     index_list.append(len(site_list))
 
-    for i in range(len(index_list) - 1):
-        start = index_list[i]  # [0]
-        end = index_list[i + 1]  # [21]
+    for start, end in zip(index_list[:-1], index_list[1:]):
 
         # grab a block containing timeseries 0:21,
         # which are all from the same site

dataretrieval/waterdata/utils.py

@@ -184,9 +184,8 @@ def _format_api_dates(
     if len(datetime_input) <= 2:
         # If the list is of length 1, first look for things like "P7D" or dates
         # already formatted in ISO08601. Otherwise, try to coerce to datetime
-        if (
-            len(datetime_input) == 1
-            and re.search(r"P", datetime_input[0], re.IGNORECASE)
+        if len(datetime_input) == 1 and (
+            re.search(r"P", datetime_input[0], re.IGNORECASE)
             or "/" in datetime_input[0]
         ):
             return datetime_input[0]
@@ -291,12 +290,15 @@ def _check_ogc_requests(endpoint: str = "daily", req_type: str = "queryables"):
 
     Raises
     ------
-    AssertionError
+    ValueError
         If req_type is not "queryables" or "schema".
     requests.HTTPError
         If the HTTP request returns an unsuccessful status code.
     """
-    assert req_type in ["queryables", "schema"]
+    if req_type not in ("queryables", "schema"):
+        raise ValueError(
+            f"req_type must be 'queryables' or 'schema', got {req_type!r}"
+        )
     url = f"{OGC_API_URL}/collections/{endpoint}/{req_type}"
     resp = requests.get(url, headers=_default_headers())
     resp.raise_for_status()