Appium Screenshot with png filename

I am trying to add activity and timestamp on PNG filename, but png file doesn’t create in my folder that I selected. Please help

import unittest
from time import sleep, strftime
from appium import webdriver

class SettingsTest(uniitest.Testcase):
    def setUp(self):
        desired_cap = {}
        self.driver = webdriver.Remote('http://localhost:4723/wd/hub', desired_cap)
    def test_settings(self):
        ts = strftime("%m/%d/%Y, %H:%M:%S")
        activity_name = self.driver.current_activity
        filename = activity_name + '_' + ts

        el = self.driver.find_element_by_android_uiautomator('new UiSelector().text("Network & internet")')
        self.driver.save_screenshot("/Users/johnd/PycharmProjects/Python/appium_JH_Project/screenshot/"+ filename + '.png')

if __name__ == '__main__':
    suite = unittest.TestLoader().loadTestsFromTestCase(SettingsTest)