No longer supporting optional values

Per:
https://stackoverflow.com/q/40989413
https://stackoverflow.com/q/36328769
https://stackoverflow.com/q/26985650
https://bugs.python.org/issue9338

render50

@@ -61,10 +61,10 @@ def main():
     parser.add_argument("-f", "--force", action="store_true", default=False, help="overwrite existing files without prompting")
     parser.add_argument("-i", "--include", action="append", help="pattern to include")
     parser.add_argument("-o", "--output", help="file to output", required=True)
-    parser.add_argument("-p", "--print", const="letter landscape", help="size of page, formatted for print, per https://developer.mozilla.org/en-US/docs/Web/CSS/@page/size", metavar="SIZE", nargs="?")
+    parser.add_argument("-p", "--print", default="letter landscape", help="format for print, per https://developer.mozilla.org/en-US/docs/Web/CSS/@page/size", metavar="SIZE")
     parser.add_argument("-P", "--no-path", action="store_true", default=False, help="omit paths in headers")
     parser.add_argument("-r", "--recursive", action="store_true", help="recurse into directories")
-    parser.add_argument("-s", "--screen", const="480p", help="size of page, formatted for screen", metavar="SIZE", nargs="?")
+    parser.add_argument("-s", "--screen", action="store_const", const="480p", help="format for screen")
     parser.add_argument("-S", "--style", default="default", help="style of syntax highlighting, per https://pygments.org/demo/#try")
     parser.add_argument("-x", "--exclude", action="append", help="pattern to exclude")
     parser.add_argument("-y", "--side-by-side", action="store_true", help="render inputs side by side")

setup.py

@@ -18,5 +18,5 @@
     python_requires=">=3.6",
     scripts=["render50"],
     url="https://github.com/cs50/render50",
-    version="8.0.3"
+    version="9.0.0"
 )