How to use the qualysapi.version.__version__ function in qualysapi

#
        # Determine API version.
        # Preformat call.
        api_call = self.preformat_call(api_call)
        if api_version:
            # API version specified, format API version inputted.
            api_version = self.format_api_version(api_version)
        else:
            # API version not specified, determine automatically.
            api_version = self.which_api_version(api_call)
        #
        # Set up base url.
        url = self.url_api_version(api_version)
        #
        # Set up headers.
        headers = {"X-Requested-With": "QualysAPI (python) v%s - VulnWhisperer" % (qualysapi.version.__version__,)}
        logger.debug('headers =\n%s' % (str(headers)))
        # Portal API takes in XML text, requiring custom header.
        if api_version in ('am', 'was', 'am2'):
            headers['Content-type'] = 'text/xml'
        #
        # Set up http request method, if not specified.
        if not http_method:
            http_method = self.format_http_method(api_version, api_call, data)
        logger.debug('http_method =\n%s' % http_method)
        #
        # Format API call.
        api_call = self.format_call(api_version, api_call)
        logger.debug('api_call =\n%s' % (api_call))
        # Append api_call to url.
        url += api_call
        #