[BEAM-2085] Fixups for Python resource hints. (#14605)

sdks/python/apache_beam/options/pipeline_options.py

@@ -447,6 +447,7 @@ def _add_argparse_args(cls, parser):
 
     parser.add_argument(
         '--resource_hint',
+        '--resource_hints',
         dest='resource_hints',
         action='append',
         default=[],

sdks/python/apache_beam/transforms/resources.py

@@ -94,15 +94,15 @@ def register_resource_hint(
   @staticmethod
   def _parse_str(value):
     if not isinstance(value, str):
-      raise ValueError()
+      raise ValueError("Input must be a string.")
     return value.encode('ascii')
 
   @staticmethod
   def _parse_int(value):
     if isinstance(value, str):
       value = int(value)
     if not isinstance(value, int):
-      raise ValueError()
+      raise ValueError("Input must be an integer.")
     return str(value).encode('ascii')
 
   @staticmethod
@@ -113,7 +113,7 @@ def _parse_storage_size_str(value):
       return ResourceHint._parse_int(value)
 
     if not isinstance(value, str):
-      raise ValueError()
+      raise ValueError("Input must be a string or integer.")
 
     value = value.strip().replace(" ", "")
     units = {
@@ -131,9 +131,11 @@ def _parse_storage_size_str(value):
     }
     match = re.match(r'.*?(\D+)$', value)
     if not match:
-      raise ValueError()
+      raise ValueError("Unrecognized value pattern.")
 
     suffix = match.group(1)
+    if suffix not in units:
+      raise ValueError("Unrecognized unit.")
     multiplier = units[suffix]
     value = value[:-len(suffix)]