4.3Inheritance: Base Page Classes

When pages share common behavior (navigation bar, footer, common waits), use a base class.

class BasePage:
    def __init__(self, driver):
        self.driver = driver
        self.wait = WebDriverWait(driver, 10)

    def get_page_title(self) -> str:
        return self.driver.title

    def is_loaded(self, locator) -> bool:
        try:
            self.wait.until(EC.presence_of_element_located(locator))
            return True
        except TimeoutException:
            return False

    def scroll_to_element(self, locator):
        element = self.driver.find_element(*locator)
        self.driver.execute_script("arguments[0].scrollIntoView(true);", element)

class LoginPage(BasePage):
    # Inherits __init__, get_page_title, is_loaded, scroll_to_element
    EMAIL = (By.CSS_SELECTOR, "input[name='email']")
    # ...

class AdminPage(BasePage):
    USER_TABLE = (By.CSS_SELECTOR, ".user-table")

    def is_loaded(self, locator=None):
        return super().is_loaded(locator or self.USER_TABLE)

The Inheritance Trap

Deep inheritance hierarchies become brittle:

# BAD: 4 levels deep — hard to understand and modify
class BasePage: ...
class AuthenticatedPage(BasePage): ...
class AdminPage(AuthenticatedPage): ...
class SuperAdminPage(AdminPage): ...

When SuperAdminPage behaves unexpectedly, you must trace through four levels to find the issue. Changes to BasePage can break all downstream classes.

Rule of thumb: Keep inheritance to one or two levels maximum.