WebDriverWait显示等待源码剖析

from selenium.webdriver.support.wait import WebDriverWait
from selenium import webdriver
driver = webdriver.Chrome()
elem = WebDriverWait(driver, 5).until(lambda driver: driver.find_element_by_id(‘su’))
elem.click()

import time
from selenium.common.exceptions import NoSuchElementException
from selenium.common.exceptions import TimeoutException

POLL_FREQUENCY = 0.5  # 没0.5秒调用一下util接收到的方法
IGNORED_EXCEPTIONS = (NoSuchElementException,)  # 忽略遇到异常


class WebDriverWait(object):
    def __init__(self, driver, timeout, poll_frequency=POLL_FREQUENCY, ignored_exceptions=None):
        """
　　　　　此处省略注释
"""
        self._driver = driver
        self._timeout = timeout
        self._poll = poll_frequency
        # avoid the divide by zero
        if self._poll == 0:
            self._poll = POLL_FREQUENCY
        exceptions = list(IGNORED_EXCEPTIONS)
        if ignored_exceptions is not None:
            try:
                exceptions.extend(iter(ignored_exceptions))
            except TypeError:  # ignored_exceptions is not iterable
                exceptions.append(ignored_exceptions)
        self._ignored_exceptions = tuple(exceptions)

    def __repr__(self):
        return ‘<{0.__module__}.{0.__name__} (session="{1}")>‘.format(
            type(self), self._driver.session_id)

    def until(self, method, message=‘‘):
        """Calls the method provided with the driver as an argument until the         return value is not False."""
        screen = None
        stacktrace = None

        end_time = time.time() + self._timeout
        while True:
            try:
                value = method(self._driver)
                if value:
                    return value
            except self._ignored_exceptions as exc:
                screen = getattr(exc, ‘screen‘, None)
                stacktrace = getattr(exc, ‘stacktrace‘, None)
            time.sleep(self._poll)
            if time.time() > end_time:
                break
        raise TimeoutException(message, screen, stacktrace)

value = method(self._driver)
if value:
   return value