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Author: serhiy-storchaka

Lib/argparse.py

@@ -937,13 +937,15 @@ def __init__(self,
             _option_strings.append(option_string)
 
             if len(option_string) > 2 and option_string[0] == option_string[1]:
+                # two-dash long option: '--foo' -> '--no-foo'
                 if option_string.startswith('no-', 2):
                     raise ValueError(f'invalid option name {option_string!r} '
                                      f'for BooleanOptionalAction')
                 option_string = option_string[:2] + 'no-' + option_string[2:]
                 _option_strings.append(option_string)
                 neg_option_strings.append(option_string)
             elif len(option_string) > 2 and option_string[0] != option_string[1]:
+                # single-dash long option: '-foo' -> '-nofoo'
                 if option_string.startswith('no', 1):
                     raise ValueError(f'invalid option name {option_string!r} '
                                      f'for BooleanOptionalAction')