getting html dynamic content python3

Here is a solution using Selenium and Firefox:

1. Open a browser window and navigating to the url
2. Waiting till the link for practice appears
3. Extracting all span elements that hold part of the text
4. Create the output string. In case the first word has only one letter there will be only 2 span elements. If the word has more than one letter there will be 3 span elements.

from selenium import webdriver
from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC


url = 'http://play.typeracer.com/'
browser = webdriver.Firefox()
browser.get(url)

try:  # waiting till link is loaded
    element = WebDriverWait(browser, 30).until(
        EC.presence_of_element_located((By.LINK_TEXT, 'Practice')))
finally:  # link loaded -> click it
    element.click()

try:  # wait till text is loaded
    WebDriverWait(browser, 30).until(
        EC.presence_of_element_located((By.XPATH, '//span[@unselectable="on"]')))
finally:  # extract text 
    spans = browser.find_elements_by_xpath('//span[@unselectable="on"]')
    if len(spans) == 2:  # first word has only one letter
        text = f'{spans[0].text} {spans[1].text}'
    elif len(spans) == 3:  # first word has more than one letter
        text = f'{spans[0].text}{spans[1].text} {spans[2].text}'
    else:
        text = ' '.join([span.text for span in spans])
        print('special case that is not handled yet: {text}')


print(text)
>>> 'Scissors cuts paper. Paper covers rock. Rock crushes lizard. Lizard poisons Spock. Spock smashes scissors. Scissors decapitates lizard. Lizard eats paper. Paper disproves Spock. Spock vaporizes rock. And as it always has, rock crushes scissors.'

Update

Just in case you also want to automate the typing afterwards ;)

try:
    txt_input = WebDriverWait(browser, 30).until(
        EC.presence_of_element_located((By.XPATH,
            '//input[@class="txtInput" and @autocorrect="off"]')))
finally:
    for letter in text:
        txt_input.send_keys(letter)

The reason for the try:... finally: ... blocks is that we have to wait till the content is loaded - which can sometimes take quite a bit.