Improve arg parsing in dump-swagger

scripts/dump-swagger.py

@@ -19,7 +19,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-
+import argparse
 import errno
 import json
 import logging
@@ -37,16 +37,24 @@ sys.path.insert(0, templating_dir)
 
 from matrix_templates import units
 
-if len(sys.argv) > 3:
-    sys.stderr.write("usage: %s [output_file] [client_release_label]\n" % (sys.argv[0],))
-    sys.exit(1)
+parser = argparse.ArgumentParser(
+    "dump-swagger.py - assemble the Swagger specs into a single JSON file"
+)
+parser.add_argument(
+    "--client_release", "-c", metavar="LABEL",
+    default="unstable",
+    help="""The client-server release version to gneerate for. Default:
+    %(default)s""",
+)
+parser.add_argument(
+    "-o", "--output",
+    default=os.path.join(scripts_dir, "swagger", "api-docs.json"),
+    help="File to write the output to. Default: %(default)s"
+)
+args = parser.parse_args()
 
-if len(sys.argv) > 1:
-    output_file = os.path.abspath(sys.argv[1])
-else:
-    output_file = os.path.join(scripts_dir, "swagger", "api-docs.json")
-
-release_label = sys.argv[2] if len(sys.argv) > 2 else "unstable"
+output_file = os.path.abspath(args.output)
+release_label = args.client_release
 
 major_version = release_label
 match = re.match("^(r\d+)(\.\d+)*$", major_version)