examples/deepzoom: enforce --format enum in argparse

Give clearer feedback if the argument is invalid.  For the WSGI programs
we need to continue enforcing validity outside of argparse, since the
value may be set by other means.

Signed-off-by: Benjamin Gilbert <bgilbert@cs.cmu.edu>

Author: bgilbert

examples/deepzoom/deepzoom_multiserver.py

@@ -356,8 +356,8 @@ def __init__(self, relpath: str):
     parser.add_argument(
         '-f',
         '--format',
-        metavar='{jpeg|png}',
         dest='DEEPZOOM_FORMAT',
+        choices=['jpeg', 'png'],
         help='image format for tiles [jpeg]',
     )
     parser.add_argument(

examples/deepzoom/deepzoom_server.py

@@ -293,8 +293,8 @@ def xfrm(img: Image.Image) -> None:
     parser.add_argument(
         '-f',
         '--format',
-        metavar='{jpeg|png}',
         dest='DEEPZOOM_FORMAT',
+        choices=['jpeg', 'png'],
         help='image format for tiles [jpeg]',
     )
     parser.add_argument(

examples/deepzoom/deepzoom_tile.py

@@ -426,9 +426,9 @@ def _shutdown(self) -> None:
     parser.add_argument(
         '-f',
         '--format',
-        metavar='{jpeg|png}',
         dest='format',
         default='jpeg',
+        choices=['jpeg', 'png'],
         help='image format for tiles [jpeg]',
     )
     parser.add_argument(