Allow specifying the datasets to download

download.py

@@ -71,9 +71,8 @@ def main():
     parser.add_argument("--resume", action="store_true", help="keep existing files in target directory")
     parser.add_argument(
         "--datasets",
-        nargs="+",
-        metavar="DATASET_CODE",
-        help="download only the given datasets (datasets codes, space separated)",
+        default=os.getenv("DATASETS"),
+        help="download only the given datasets (datasets codes, comma separated)",
     )
     args = parser.parse_args()
 
@@ -88,13 +87,19 @@ def main():
     log.info("Command-line arguments: %r", args)
 
     if args.from_datetime is None:
-        log.info("Argument --from-datetime was not provided: all datasets will be downloaded")
+        log.info(
+            "Argument --from-datetime was not provided: "
+            "the requested datasets will be downloaded without taking their update date into account"
+        )
     else:
         log.info(
             "Argument --from-datetime=%r: only datasets that changed since that datetime will be downloaded",
             args.from_datetime.isoformat(),
         )
 
+    if args.datasets is not None:
+        args.datasets = args.datasets.split(",")
+
     toc_file_name = "table_of_contents.xml"
     toc_file = args.target_dir / toc_file_name
     if args.resume and toc_file.is_file():