How can I dynamically create an xpath string in Python for a webdriver xpath selector?

Question

I am writing a Selenium Webdriver test using python2.7 to use XPath to select a link node set. For each link, I need to change the href attribute using driver.execute_script to execute javascript.

Trying to build the XPath string to vary the index in a separate loop.

The original statement which I need to build as a string and vary the index in a separate loop:

elem2 = driver.find_element_by_xpath("(//a[contains(text(),'Comment')])[3]") 
xp_str1 = str("\"(//a[contains(text(),'Comment')])[")
xp_str2 = str(3)
xp_str3 = str("]\"")
str_elem = xp_str1 + xp_str2 + xp_str3
elem2 = driver.find_element_by_xpath(str_elem) 
driver.execute_script("arguments[0].href = 'social_media/comment/type/peer/id/9999';", elem2)

I consistently get the webdriver error:

 InvalidSelectorException: Message: u'The given selector " //a[contains(text(),\'Comment\')])[3]" is either invalid or does not result in a WebElement. The following error occurred:\nInvalidSelectorError: Unable to locate an element with the xpath expression "(//a[contains(text(),\'Comment\')])[3]" because of the following error:\n[Exception... "The expression cannot be converted to return the specified type." code: "0" nsresult: "0x805b0034 (TypeError)"

Can any one give me ideas?

• Mark Mayo: So your original statement works, but you're having trouble putting it into a loop?
• anthony: The original statement works for each node in the set. I would like to dynamically generate the xpath string in order to vary the index (in this instance [3]) and test each member of the set. The loop shouldn't be a problem, but concatenating the xpath string and using it as a string variable with webdriver (str_elem), seems to be a problem.

Answer 1

I seems for me that you have too much quotation marks in here. I think

xp_str1 = str("//a[contains(text(),'Comment')])[")
xp_str2 = str(3)
xp_str3 = str("]")
str_elem = xp_str1 + xp_str2 + xp_str3

fixes this because when you use

driver.find_element_by_xpath("(//a[contains(text(),'Comment')])[3]") 

quotation marks mean that argument or function is a string. And when you use

driver.find_element_by_xpath(str_elem)

the argument for function is string variable, so you don't need additional quotation marks.

Answer 2

The problem looks (from the error) like it may have something to do with the extra '(' in your selector. Given you state the original statement works:

elem2 = driver.find_element_by_xpath("(//a[contains(text(),'Comment')])[3]")

and this is the bad one:

The given selector "(//a[contains(text(),\'Comment\')])[3]"

you can clearly see the difference when lined up. You appear to have an extra '(' at the start.

I believe

xp_str1 = str("\"//a[contains(text(),'Comment')])[")
xp_str2 = str(3)
xp_str3 = str("]\"")
str_elem = xp_str1 + xp_str2 + xp_str3

may fix that. I just tried it quickly in an online interpreter, and it appears to fix it.

• anthony: Thanks for the response. Using the string assignment str_elem after removing the extra '(', still gives the same error. In fact without that '(', the syntax becomes unbalanced in the final string, the opening parentheses are 2 and the closing parentheses are 3. My problem remains.