You can easily get the page source in Selenium via the page_source attribute of the Selenium web driver.
Here is some sample code for getting the page source of the ScrapingBee website:
from selenium import webdriver
DRIVER_PATH = '/path/to/chromedriver'
driver = webdriver.Chrome(executable_path=DRIVER_PATH)
driver.get("http://www.scrapingbee.com")
# Print page source on screen
print(driver.page_source)