Registers a boolean flag.

Such a boolean flag does not take an argument. If a user wants to specify a false value explicitly, the long option beginning with 'no' must be used: i.e. --noflag

This flag will have a value of None, True or False. None is possible if default=None and the user does not specify the flag on the command line.

name str, the flag name.
default bool|str|None, the default value of the flag.
help str, the help message.
flag_values FlagValues, the FlagValues instance with which the flag will be registered. This should almost never need to be overridden.
module_name str, the name of the Python module declaring this flag. If not provided, it will be computed using the stack trace of this call.
**args dict, the extra keyword args that are passed to Flag init.

a handle to defined flag.