foreword
When locating elements, various exceptions are often encountered. Why do these exceptions occur, and how should they be handled?
This article learns the reason for exceptions by learning the exceptions module of selenium.
1. An exception occurs
1. Open the blog homepage, locate the "New Post" element, this element id=" blog_nav_newpost"
2. In order to intentionally make it fail to locate, I add xx after the element attribute
3. After the operation fails, as shown in the figure below, the program is interrupted in the line where the element is found, and the click event will not continue to be executed.
2. Catch exceptions
1. In order to let the program continue to execute, we can use try...except... to catch the exception. After the exception is caught, the cause of the exception can be printed out, so as to facilitate the analysis of the cause of the exception
2. As can be seen from the following exception content, the cause of the exception is: NoSuchElementException
selenium.common.exceptions.NoSuchElementException: Message: Unable to locate element: {"method":"id","selector":"blog_nav_newpostxx"}
3. Import the NoSuchElementException class from selenium.common.exceptions
3. Reference code:
# coding:utf-8
from selenium import webdriver
from selenium.common.exceptions import NoSuchElementException
driver = webdriver.Firefox()
driver.get("http://www.cnblogs.com/yoyoketang/")
# Locate the home page "New Essay "
try:
element = driver.find_element("id", "blog_nav_newpostxx")
except NoSuchElementException as msg:
print u"Find element exception %s"%msg
# Click on the element # Exchange QQ group: 232607095
else:
element.click()
Fourth, selenium common exceptions
1.NoSuchElementException: No element found
2.NoSuchFrameException: No iframe found
3.NoSuchWindowException: No window handle found
4.NoSuchAttributeException: attribute error
5.NoAlertPresentException: No alert popup found
6.lementNotVisibleException: Element is not visible
7. ElementNotSelectableException: Element is not selected
8. TimeoutException: Timeout to find element
5. Other exceptions and source code
1. In the Lib directory: \Lib\site-packages\selenium\common If you are interested, you can take a look
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# KIND, either express or implied. See the License for the
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"""
Exceptions that may happen in all the webdriver code.
"""
class WebDriverException(Exception):
"""
Base webdriver exception.
"""
def __init__(self, msg=None, screen=None, stacktrace=None):
self.msg = msg
self.screen = screen
self.stacktrace = stacktrace
def __str__(self):
exception_msg = "Message: %s\n" % self.msg
if self.screen is not None:
exception_msg += "Screenshot:available via screen\n"
if self.stacktrace is not None:
stacktrace = "\n".join(self.stacktrace)
exception_msg += "Stacktrace:\n%s" % stacktrace
return exception_msg
class ErrorInResponseException(WebDriverException):
"""
Thrown when an error has occurred on the server side.
This may happen when communicating with the firefox extension
or the remote driver server.
"""
def __init__(self, response, msg):
WebDriverException.__init__(self, msg)
self.response = response
class InvalidSwitchToTargetException(WebDriverException):
"""
Thrown when frame or window target to be switched doesn't exist.
"""
pass
class NoSuchFrameException(InvalidSwitchToTargetException):
"""
Thrown when frame target to be switched doesn't exist.
"""
pass
class NoSuchWindowException(InvalidSwitchToTargetException):
"""
Thrown when window target to be switched doesn't exist.
To find the current set of active window handles, you can get a list
of the active window handles in the following way::
print driver.window_handles
"""
pass
class NoSuchElementException(WebDriverException):
"""
Thrown when element could not be found.
If you encounter this exception, you may want to check the following:
* Check your selector used in your find_by...
* Element may not yet be on the screen at the time of the find operation,
(webpage is still loading) see selenium.webdriver.support.wait.WebDriverWait()
for how to write a wait wrapper to wait for an element to appear.
"""
pass
class NoSuchAttributeException(WebDriverException):
"""
Thrown when the attribute of element could not be found.
You may want to check if the attribute exists in the particular browser you are
testing against. Some browsers may have different property names for the same
property. (IE8's .innerText vs. Firefox .textContent)
"""
pass
class StaleElementReferenceException(WebDriverException):
"""
Thrown when a reference to an element is now "stale".
Stale means the element no longer appears on the DOM of the page.
Possible causes of StaleElementReferenceException include, but not limited to:
* You are no longer on the same page, or the page may have refreshed since the element
was located.
* The element may have been removed and re-added to the screen, since it was located.
Such as an element being relocated.
This can happen typically with a javascript framework when values are updated and the
node is rebuilt.
* Element may have been inside an iframe or another context which was refreshed.
"""
pass
class InvalidElementStateException(WebDriverException):
"""
"""
pass
class UnexpectedAlertPresentException(WebDriverException):
"""
Thrown when an unexpected alert is appeared.
Usually raised when when an expected modal is blocking webdriver form executing any
more commands.
"""
def __init__(self, msg=None, screen=None, stacktrace=None, alert_text=None):
super(UnexpectedAlertPresentException, self).__init__(msg, screen,stacktrace)
self.alert_text = alert_text
def __str__(self):
return "Alert Text: %s\n%s" % (self.alert_text, super(UnexpectedAlertPresentException, self).__str__())
class NoAlertPresentException(WebDriverException):
"""
Thrown when switching to no presented alert.
This can be caused by calling an operation on the Alert() class when an alert is
not yet on the screen.
"""
pass
class ElementNotVisibleException(InvalidElementStateException):
"""
Thrown when an element is present on the DOM, but
it is not visible, and so is not able to be interacted with.
Most commonly encountered when trying to click or read text
of an element that is hidden from view.
"""
pass
class ElementNotSelectableException(InvalidElementStateException):
"""
Thrown when trying to select an unselectable element.
For example, selecting a 'script' element.
"""
pass
class InvalidCookieDomainException(WebDriverException):
"""
Thrown when attempting to add a cookie under a different domain
than the current URL.
"""
pass
class UnableToSetCookieException(WebDriverException):
"""
Thrown when a driver fails to set a cookie.
"""
pass
class RemoteDriverServerException(WebDriverException):
"""
"""
pass
class TimeoutException(WebDriverException):
"""
Thrown when a command does not complete in enough time.
"""
pass
class MoveTargetOutOfBoundsException(WebDriverException):
"""
Thrown when the target provided to the `ActionsChains` move()
method is invalid, i.e. out of document.
"""
pass
class UnexpectedTagNameException(WebDriverException):
"""
Thrown when a support class did not get an expected web element.
"""
pass
class InvalidSelectorException(NoSuchElementException):
"""
Thrown when the selector which is used to find an element does not return
a WebElement. Currently this only happens when the selector is an xpath
expression and it is either syntactically invalid (i.e. it is not a
xpath expression) or the expression does not select WebElements
(e.g. "count(//input)").
"""
pass
class ImeNotAvailableException(WebDriverException):
"""
Thrown when IME support is not available. This exception is thrown for every IME-related
method call if IME support is not available on the machine.
"""
pass
class ImeActivationFailedException(WebDriverException):
"""
Thrown when activating an IME engine has failed.
"""
pass