@staticmethod
def _unpack_arg(_arg):
    """ Returns the interior of the parenthesis of an argument.

        'arg(value)'     -> 'arg', 'value'
        'arg("value")'   -> 'arg', 'value'
        'arg('value')'   -> 'arg', 'value'
        'arg'            -> 'arg', ''
        '"arg"'          -> 'arg', ''
        ''arg''          -> 'arg', ''

        Any quotes will be stripped from the value.
        Any whitespaces will be stripped from the value or arg.

        If there is no value given, simply the _arg is returned and an empty string for the value.

        example:
        >>> ExecParser._unpack_arg("bolus(2.00)")
        ('bolus', '2.00')

        """
    if '(' in _arg:
        _val = _arg[_arg.find('(') + 1:_arg.find(')')].strip('"').strip("'"
            ).strip()
        _arg = _arg[0:_arg.find('(')].strip()
    else:
        _val = ''
        _arg = _arg.strip('"').strip("'").strip()
    return _arg, _val
