def natural(value, argument='<STR_LIT>'):
value = _get_integer(value)<EOL>if value < <NUM_LIT:0>:<EOL><INDENT>error = ('<STR_LIT>'<EOL>'<STR_LIT>'.format(arg=argument, value=value))<EOL>raise ValueError(error)<EOL><DEDENT>return value<EOL>
Restrict input type to the natural numbers (0, 1, 2, 3...)