By the selenium.webdriver.common.by

By positioning support:

1. CLASS_NAME = 'class name'
2. CSS_SELECTOR = 'css selector'
3. ID = 'id'
4. LINK_TEXT = 'link text'
5. NAME = 'name'
6. PARTIAL_LINK_TEXT = 'partial link text'
7. TAG_NAME = 'tag name'
8. XPATH = 'xpath'

Import by:

from selenium.webdriver.common.by import By

usage:

# User name input box
element=(By.ID,'user_name')