<div id="loader-mid" style="position: absolute; top: 118.5px; left: 554px; display: none;">
    <div class="a">Loading</div>
    <div class="b">please wait...</div>
</div>

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

self.wait = WebDriverWait(driver, 10)

self.wait.until(EC.invisibility_of_element_located((By.XPATH, "//*[@id='loader_mid'][contains(@style, 'display: block')]")))

self.wait.until_not(EC.presence_of_element_located((By.XPATH, "//*[@id='loader_mid'][contains(@style, 'display: block')]")))

SHORT_TIMEOUT  = 5   # give enough time for the loading element to appear
LONG_TIMEOUT = 30  # give enough time for loading to finish
LOADING_ELEMENT_XPATH = '//*[@id="xPath"]/xPath/To/The/Loading/Element'

try:
    # wait for loading element to appear
    # : need to make sure we don't prematurely check if element
    # : has disappeared before it has had a chance to appear
    WebDriverWait(
            driver, SHORT_TIMEOUT
    ).until(EC.presence_of_element_located((By.XPATH, LOADING_ELEMENT_XPATH)))

    # then wait for it to disappear
    WebDriverWait(
            driver, LONG_TIMEOUT
    ).until_not(EC.presence_of_element_located((By.XPATH, LOADING_ELEMENT_XPATH)))

except TimeoutException:
    # if timeout exception was raised - should be safe to assume loading has finished.
    # : However this may not always be the case, use with caution, othwise handle appropriately.
    pass

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

while True:
        try:
            WebDriverWait(driver, 1).until(EC.presence_of_element_located((By.XPATH, 'your_xpath')))
        except TimeoutException:
            break