Add backup URL fallback for CTX index and minor improvements

- CTXIndex: Add backup URL (pdsimage2.wr.usgs.gov) with automatic fallback
- CTXIndex: Track successful URL for constructing downstream URLs
- index_main.py: Clean up imports
- ctx_calib.py: Add optional fname parameter to write_isis_filelist

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: michaelaye

src/planetarypy/instruments/mro/ctx/ctx_calib.py

@@ -549,10 +549,12 @@ def image_list_lev2_path(self):
         "get the path to the image list file"
         return self.workdir / "image_list_lev2.lis"
 
-    def write_isis_filelist(self, workdir=None, level=1):
+    def write_isis_filelist(self, workdir=None, fname=None, level=1):
         workdir = self.workdir if workdir is None else Path(workdir)
         logger.debug(f"{self.workdir=}")
-        savepath = workdir / f"image_list_lev{level}.lis"
+        savepath = (
+            workdir / f"image_list_lev{level}.lis" if fname is None else workdir / fname
+        )
         match level:
             case 0:
                 paths = self.cub_paths

src/planetarypy/pds/dynamic_url_handlers.py

@@ -4,24 +4,52 @@
 __all__ = ["CTXIndex", "LROCIndex"]
 
 import pandas as pd
+from loguru import logger
 from yarl import URL
 
 
 class CTXIndex:
     url = "https://planetarydata.jpl.nasa.gov/img/data/mro/ctx/"
+    backup_url = "https://pdsimage2.wr.usgs.gov/Mars_Reconnaissance_Orbiter/CTX"
 
     def __init__(self):
         self._volumes_table = None
+        self._successful_url = None
 
     @property
     def volumes_table(self):
         if self._volumes_table is None:
-            self._volumes_table = (
-                pd.read_html(self.url)[0]
-                .dropna(how="all", axis=1)
-                .dropna(how="all", axis=0)
-                .iloc[1:, :-1]
-            )
+            # Try primary URL first
+            try:
+                self._volumes_table = (
+                    pd.read_html(self.url)[0]
+                    .dropna(how="all", axis=1)
+                    .dropna(how="all", axis=0)
+                    .iloc[1:, :-1]
+                )
+                self._successful_url = self.url
+            except Exception as e:
+                # If primary URL fails, try backup URL
+                logger.warning(
+                    f"Failed to fetch CTX volumes table from primary URL {self.url}: {e}. "
+                    f"Trying backup URL {self.backup_url}."
+                )
+                try:
+                    self._volumes_table = (
+                        pd.read_html(self.backup_url)[0]
+                        .dropna(how="all", axis=1)
+                        .dropna(how="all", axis=0)
+                        .iloc[1:, :-1]
+                    )
+                    self._successful_url = self.backup_url
+                    logger.info(
+                        "Successfully fetched CTX volumes table from backup URL"
+                    )
+                except Exception as backup_error:
+                    logger.error(
+                        f"Failed to fetch CTX volumes table from backup URL {self.backup_url}: {backup_error}"
+                    )
+                    raise backup_error
         return self._volumes_table
 
     @property
@@ -34,7 +62,9 @@ def latest_release_number(self):
 
     @property
     def latest_index_label_url(self):
-        return URL(self.url) / f"{self.latest_release_folder}index/cumindex.lbl"
+        # Use the successful URL (primary or backup) for constructing the label URL
+        base_url = self._successful_url if self._successful_url else self.url
+        return URL(base_url) / f"{self.latest_release_folder}index/cumindex.lbl"
 
 
 class LROCIndex:

src/planetarypy/pds/index_main.py

@@ -5,21 +5,20 @@
 
 __all__ = ["Index", "InventoryIndex"]
 
-from pathlib import Path
 import csv
-import pandas as pd
+from pathlib import Path
 
+import pandas as pd
 from loguru import logger
 from yarl import URL
 
 from ..config import config
-from ..utils import url_retrieve, have_internet
-
-from .index_labels import IndexLabel
+from ..utils import have_internet, url_retrieve
 from .dynamic_index import (
-    DYNAMIC_URL_HANDLERS,
+    DYNAMIC_URL_HANDLERS,  # registry of dynamic index handlers
     DynamicRemoteHandler,
 )
+from .index_labels import IndexLabel
 from .static_index import StaticRemoteHandler