Improve usage help messaging.

diff --git a/stable.py b/stable.py
index d32f7681e6c0c628721a9630e459b5ce1ad93386..26bb8e4243fb2702caee36e808b217736a3fea07 100755 (executable)
--- a/stable.py
+++ b/stable.py
@@ -1,12 +1,12 @@
 #!/usr/bin/env python3
-from sys import exit as sys_exit
+from sys import argv, exit as sys_exit
 from os.path import dirname, basename, splitext, join as path_join, exists
 from argparse import ArgumentParser
 from random import randint
 from stable.core import ImageMaker
 
 
-DEFAULT_SCHEDULER='EulerAncestralDiscreteScheduler'
+DEFAULT_SCHEDULER = 'EulerAncestralDiscreteScheduler'
 
 
 def save_path(count: int) -> str:
@@ -20,11 +20,13 @@ def parse_args():
     parser.add_argument('-o', '--output')
     parser.add_argument('-p', '--prompt')
     parser.add_argument('-H', '--help', action='help')
-    parser.add_argument('-S', '--list_schedulers', action='store_true')
-    parser.add_argument('-g', '--guidance', default=7.5, type=float,
-                        help='default: 7.5')
+    parser.add_argument('-S', '--list-schedulers', action='store_true')
     parser.add_argument('-h', '--height', default=512, type=int,
                         help='default: 512')
+    parser.add_argument('-w', '--width', default=512, type=int,
+                        help='default: 512')
+    parser.add_argument('-g', '--guidance', default=7.5, type=float,
+                        help='default: 7.5')
     parser.add_argument('-n', '--n_steps', default=15, type=int,
                         help='default: 15')
     parser.add_argument('-q', '--quantity', default=1, type=int,
@@ -32,15 +34,22 @@ def parse_args():
     parser.add_argument('-r', '--randomness_seed', default=1, type=int,
                         help='default: 1; if set 0, chosen randomnly')
     parser.add_argument('-s', '--scheduler', default=DEFAULT_SCHEDULER,
-                        help=f'default: DEFAULT_SCHEDULER')
-    parser.add_argument('-w', '--width', default=512, type=int,
-                        help='default: 512')
+                        help=f'default: {DEFAULT_SCHEDULER}')
     parsed_args = parser.parse_args()
     if not parsed_args.list_schedulers:
-        if not parsed_args.output:
-            raise Exception('Unless -H or -S, need --output set.')
-        if not parsed_args.prompt:
-            raise Exception('Unless -H or -S, need --prompt set.')
+        prefix = f'{argv[0]}: error: unless calling with -H/--help or '\
+                '-S/--list-schedulers, requiring '
+        suffix = ''
+        if (not parsed_args.output) and (not parsed_args.prompt):
+            suffix = '-o/--output and -p/--prompt'
+        elif not parsed_args.output:
+            suffix = '-o/--output'
+        elif not parsed_args.prompt:
+            suffix = '-p/--prompt'
+        if (not parsed_args.output) or (not parsed_args.prompt):
+            parser.print_usage()
+            print(f'{prefix}{suffix}')
+            sys_exit(1)
     return parsed_args