Selenium2+python自动化42-判断元素（expected_conditions）

Posted 2020-11-03 jason89

前言

经常有小伙伴问，如何判断一个元素是否存在，如何判断alert弹窗出来了，如何判断动态的元素等等一系列的判断，在selenium的expected_conditions模块收集了一系列的场景判断方法，这些方法是逢面试必考的！！！

expected_conditions一般也简称EC，本篇先介绍下有哪些功能，后续更新中会单个去介绍。

一、功能介绍和翻译

title_is： 判断当前页面的title是否完全等于（==）预期字符串，返回布尔值

title_contains : 判断当前页面的title是否包含预期字符串，返回布尔值

presence_of_element_located : 判断某个元素是否被加到了dom树里，并不代表该元素一定可见

visibility_of_element_located : 判断某个元素是否可见. 可见代表元素非隐藏，并且元素的宽和高都不等于0

visibility_of : 跟上面的方法做一样的事情，只是上面的方法要传入locator，这个方法直接传定位到的element就好了

presence_of_all_elements_located : 判断是否至少有1个元素存在于dom树中。举个例子，如果页面上有n个元素的class都是‘column-md-3‘，那么只要有1个元素存在，这个方法就返回True

text_to_be_present_in_element : 判断某个元素中的text是否 包含 了预期的字符串

text_to_be_present_in_element_value : 判断某个元素中的value属性是否 包含 了预期的字符串

frame_to_be_available_and_switch_to_it : 判断该frame是否可以switch进去，如果可以的话，返回True并且switch进去，否则返回False

invisibility_of_element_located : 判断某个元素中是否不存在于dom树或不可见

element_to_be_clickable : 判断某个元素中是否可见并且是enable的，这样的话才叫clickable

staleness_of : 等某个元素从dom树中移除，注意，这个方法也是返回True或False

element_to_be_selected : 判断某个元素是否被选中了,一般用在下拉列表

element_selection_state_to_be : 判断某个元素的选中状态是否符合预期

element_located_selection_state_to_be : 跟上面的方法作用一样，只是上面的方法传入定位到的element，而这个方法传入locator

alert_is_present : 判断页面上是否存在alert

 

二、查看源码和注释

1.打开python里这个目录l可以找到：Lib\\site-packages\\selenium\\webdriver\\support\\expected_conditions.py

  1 from selenium.common.exceptions import NoSuchElementException
  2 from selenium.common.exceptions import NoSuchFrameException
  3 from selenium.common.exceptions import StaleElementReferenceException
  4 from selenium.common.exceptions import WebDriverException
  5 from selenium.common.exceptions import NoAlertPresentException
  6 
  7 """
  8  * Canned "Expected Conditions" which are generally useful within webdriver
  9  * tests.
 10 """
 11 
 12 
 13 class title_is(object):
 14     """An expectation for checking the title of a page.
 15     title is the expected title, which must be an exact match
 16     returns True if the title matches, false otherwise."""
 17     def __init__(self, title):
 18         self.title = title
 19 
 20     def __call__(self, driver):
 21         return self.title == driver.title
 22 
 23 
 24 class title_contains(object):
 25     """ An expectation for checking that the title contains a case-sensitive
 26     substring. title is the fragment of title expected
 27     returns True when the title matches, False otherwise
 28     """
 29     def __init__(self, title):
 30         self.title = title
 31 
 32     def __call__(self, driver):
 33         return self.title in driver.title
 34 
 35 
 36 class presence_of_element_located(object):
 37     """ An expectation for checking that an element is present on the DOM
 38     of a page. This does not necessarily mean that the element is visible.
 39     locator - used to find the element
 40     returns the WebElement once it is located
 41     """
 42     def __init__(self, locator):
 43         self.locator = locator
 44 
 45     def __call__(self, driver):
 46         return _find_element(driver, self.locator)
 47 
 48 
 49 class visibility_of_element_located(object):
 50     """ An expectation for checking that an element is present on the DOM of a
 51     page and visible. Visibility means that the element is not only displayed
 52     but also has a height and width that is greater than 0.
 53     locator - used to find the element
 54     returns the WebElement once it is located and visible
 55     """
 56     def __init__(self, locator):
 57         self.locator = locator
 58 
 59     def __call__(self, driver):
 60         try:
 61             return _element_if_visible(_find_element(driver, self.locator))
 62         except StaleElementReferenceException:
 63             return False
 64 
 65 
 66 class visibility_of(object):
 67     """ An expectation for checking that an element, known to be present on the
 68     DOM of a page, is visible. Visibility means that the element is not only
 69     displayed but also has a height and width that is greater than 0.
 70     element is the WebElement
 71     returns the (same) WebElement once it is visible
 72     """
 73     def __init__(self, element):
 74         self.element = element
 75 
 76     def __call__(self, ignored):
 77         return _element_if_visible(self.element)
 78 
 79 
 80 def _element_if_visible(element, visibility=True):
 81     return element if element.is_displayed() == visibility else False
 82 
 83 
 84 class presence_of_all_elements_located(object):
 85     """ An expectation for checking that there is at least one element present
 86     on a web page.
 87     locator is used to find the element
 88     returns the list of WebElements once they are located
 89     """
 90     def __init__(self, locator):
 91         self.locator = locator
 92 
 93     def __call__(self, driver):
 94         return _find_elements(driver, self.locator)
 95 
 96 
 97 class visibility_of_any_elements_located(object):
 98     """ An expectation for checking that there is at least one element visible
 99     on a web page.
100     locator is used to find the element
101     returns the list of WebElements once they are located
102     """
103     def __init__(self, locator):
104         self.locator = locator
105 
106     def __call__(self, driver):
107         return [element for element in _find_elements(driver, self.locator) if _element_if_visible(element)]
108 
109 
110 class text_to_be_present_in_element(object):
111     """ An expectation for checking if the given text is present in the
112     specified element.
113     locator, text
114     """
115     def __init__(self, locator, text_):
116         self.locator = locator
117         self.text = text_
118 
119     def __call__(self, driver):
120         try:
121             element_text = _find_element(driver, self.locator).text
122             return self.text in element_text
123         except StaleElementReferenceException:
124             return False
125 
126 
127 class text_to_be_present_in_element_value(object):
128     """
129     An expectation for checking if the given text is present in the element‘s
130     locator, text
131     """
132     def __init__(self, locator, text_):
133         self.locator = locator
134         self.text = text_
135 
136     def __call__(self, driver):
137         try:
138             element_text = _find_element(driver,
139                                          self.locator).get_attribute("value")
140             if element_text:
141                 return self.text in element_text
142             else:
143                 return False
144         except StaleElementReferenceException:
145                 return False
146 
147 
148 class frame_to_be_available_and_switch_to_it(object):
149     """ An expectation for checking whether the given frame is available to
150     switch to.  If the frame is available it switches the given driver to the
151     specified frame.
152     """
153     def __init__(self, locator):
154         self.frame_locator = locator
155 
156     def __call__(self, driver):
157         try:
158             if isinstance(self.frame_locator, tuple):
159                 driver.switch_to.frame(_find_element(driver,
160                                                      self.frame_locator))
161             else:
162                 driver.switch_to.frame(self.frame_locator)
163             return True
164         except NoSuchFrameException:
165             return False
166 
167 
168 class invisibility_of_element_located(object):
169     """ An Expectation for checking that an element is either invisible or not
170     present on the DOM.
171 
172     locator used to find the element
173     """
174     def __init__(self, locator):
175         self.locator = locator
176 
177     def __call__(self, driver):
178         try:
179             return _element_if_visible(_find_element(driver, self.locator), False)
180         except (NoSuchElementException, StaleElementReferenceException):
181             # In the case of NoSuchElement, returns true because the element is
182             # not present in DOM. The try block checks if the element is present
183             # but is invisible.
184             # In the case of StaleElementReference, returns true because stale
185             # element reference implies that element is no longer visible.
186             return True
187 
188 
189 class element_to_be_clickable(object):
190     """ An Expectation for checking an element is visible and enabled such that
191     you can click it."""
192     def __init__(self, locator):
193         self.locator = locator
194 
195     def __call__(self, driver):
196         element = visibility_of_element_located(self.locator)(driver)
197         if element and element.is_enabled():
198             return element
199         else:
200             return False
201 
202 
203 class staleness_of(object):
204     """ Wait until an element is no longer attached to the DOM.
205     element is the element to wait for.
206     returns False if the element is still attached to the DOM, true otherwise.
207     """
208     def __init__(self, element):
209         self.element = element
210 
211     def __call__(self, ignored):
212         try:
213             # Calling any method forces a staleness check
214             self.element.is_enabled()
215             return False
216         except StaleElementReferenceException:
217             return True
218 
219 
220 class element_to_be_selected(object):
221     """ An expectation for checking the selection is selected.
222     element is WebElement object
223     """
224     def __init__(self, element):
225         self.element = element
226 
227     def __call__(self, ignored):
228         return self.element.is_selected()
229 
230 
231 class element_located_to_be_selected(object):
232     """An expectation for the element to be located is selected.
233     locator is a tuple of (by, path)"""
234     def __init__(self, locator):
235         self.locator = locator
236 
237     def __call__(self, driver):
238         return _find_element(driver, self.locator).is_selected()
239 
240 
241 class element_selection_state_to_be(object):
242     """ An expectation for checking if the given element is selected.
243     element is WebElement object
244     is_selected is a Boolean."
245     """
246     def __init__(self, element, is_selected):
247         self.element = element
248         self.is_selected = is_selected
249 
250     def __call__(self, ignored):
251         return self.element.is_selected() == self.is_selected
252 
253 
254 class element_located_selection_state_to_be(object):
255     """ An expectation to locate an element and check if the selection state
256     specified is in that state.
257     locator is a tuple of (by, path)
258     is_selected is a boolean
259     """
260     def __init__(self, locator, is_selected):
261         self.locator = locator
262         self.is_selected = is_selected
263 
264     def __call__(self, driver):
265         try:
266             element = _find_element(driver, self.locator)
267             return element.is_selected() == self.is_selected
268         except StaleElementReferenceException:
269             return False
270 
271 
272 class alert_is_present(object):
273     """ Expect an alert to be present."""
274     def __init__(self):
275         pass
276 
277     def __call__(self, driver):
278         try:
279             alert = driver.switch_to.alert
280             alert.text
281             return alert
282         except NoAlertPresentException:
283             return False
284 
285 
286 def _find_element(driver, by):
287     """Looks up an element. Logs and re-raises ``WebDriverException``
288     if thrown."""
289     try:
290         return driver.find_element(*by)
291     except NoSuchElementException as e:
292         raise e
293     except WebDriverException as e:
294         raise e
295 
296 
297 def _find_elements(driver, by):
298     try:
299         return driver.find_elements(*by)
300     except WebDriverException as e:
301         raise e

 

本篇的判断方法和场景很多，先贴出来，后面慢慢更新，详细讲解每个的功能的场景和用法。

这些方法是写好自动化脚本，提升性能的必经之路，想做好自动化，就得熟练掌握。