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How To Repair The Error With Unregistered Xpath Selector Operate

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Over the previous few weeks, a few of our customers reported that there was an error with an unregistered xpath selector perform.

 

 

   

I’m making an attempt to get src from HTML. I’ve the worth previous then I’m making an attempt to get the picture

  company_name = "mediamarkt"response.xpath (f '// img [lowercase (@alt) = "{company_name.lower ()}"]') #Errorresponse.xpath (f "// img [matches (@alt, '{company name}', 'i')]") # Error 

I get error:

  Traceback (final name final):  File "/house/timmy/.native/lib/python3.8/site-packages/parsel/selector.py" line 254 in xpath    End result = xpathev (question, namespaces = nsp,  File "src / lxml / etree.pyx", line 1582, at lxml.etree._Element.xpath  File "src / lxml / xpath.pxi", line 305, in lxml.etree.XPathElementEvaluator .__ call__  File "src / lxml / xpath.pxi", line 225, in lxml.etree._XPathEvaluatorBase._handle_resultlxml.etree.XPathEvalError: perform not registeredAnother exception occurred whereas dealing with the above exception:Traceback (final name final):  File "/usr/lib/python3.8/code.py", line 90, within the execution code    exec (code, self.locals)  File "", line 1, in   File "/house/timmy/.native/lib/python3.8/site-packages/scrapy/http/response/textual content.py" line 117 in xpath    return self.selector.xpath (question, ** kwargs)  File "/house/timmy/.native/lib/python3.8/site-packages/parsel/selector.py", line 260, in xpath    six.reraise (ValueError, ValueError (msg), sys.exc_info () [2])  File "/usr/lib/python3/dist-packages/six.py" line 702 restart    improve the worth. with_traceback (tb)  File "/house/timmy/.native/lib/python3.8/site-packages/parsel/selector.py" line 254 in xpath    End result = xpathev (question, namespaces = nsp,  File "src / lxml / etree.pyx", line 1582, at lxml.etree._Element.xpath  File "src / lxml / xpath.pxi", line 305, in lxml.etree.XPathElementEvaluator .__ call__  File "src / lxml / xpath.pxi", line 225, in lxml.etree._XPathEvaluatorBase._handle_resultValueError: XPath error: perform not registered in // img [matches (@ old, 'mediamarkt', 'i')] 

I received this XPath on account of caseless matching in xpath?

What Is XPath?

The complete title of XPath is XML Path Language, XML Path Language, a language used to search out info in XML (HTML) paperwork. It has 4 features:

  • XPath makes use of path expressions to view XML paperwork.
  • XPath incorporates the usual library
  • XPath is the core XSLT component
  • XPath is a W3C commonplace.

Technique Xpath ()

For ElementTree, the xpath methodology makes a worldwide XPath question forDocument (if absolute) or root-relative (if relative):

If xpath () is used on a component, the XPath expression is evaluatedagainst elecop (if relative) or versus household tree (if absolute):

The xpath () methodology helps XPath variables:

 >>> f = StringIO ('   ')>>> tree = etree.parse (f)>>> r = tree.xpath ('/ foo / bar')>>> len (r)one>>> r [0]. day'Bar'>>> r = tree.xpath ('bar')>>> r [0]. day'Bar'
 >>> root = tree.getroot ()>>> r = root.xpath ('stripe')>>> r [0]. day'Bar'>>> bar = root [0]>>> r = bar.xpath ('/ foo / bar')>>> r [0]. day'Bar'>>> tree = bar.getroottree ()>>> r = tree.xpath ('/ foo / bar')>>> r [0]. day'Bar'

there was an error with the xpath selector unregistered function

 >>> expr = "// * [local-name () = $ name]">>> print (root.xpath (expression, title = "foo") [0] .tag)ugh>>> print (root.xpath (expression, title = "bar") [0] .tag)bar>>> print (root.xpath ("$ textual content", textual content = "Hey everybody!"))Hey World!

Namespaces And Prefixes

In case your XPath expression makes use of namespace prefixes, you have to outline themin prefix matching. To do that, give a dictionaryThe key phrase argument Namespaces , which shows the namespace prefixes usedin XPath expression for namespace URI:

The prefixes chosen right here usually are not associated to the prefixes usedin the XML doc. Doc can outline all prefixesFor instance together with an empty prefix with out breaking the above code.

Notice that XPath doesn’t have a typical namespace. thenSo empty prefix is ​​not outlined for XPath and can’t be used inNamespace prefix mappings.

There may be additionally an non-obligatory argument for extension which is usedDefine customized extension features native to them in Python.Evaluation. The namespace prefixes they use in XPathThe expression should even be outlined within the namespace prefix map.

 >>> f = StringIO ('' 'n... ...  Textual content ... ... '' ')>>> doc = etree.parse (f)>>> r = doc.xpath ('/ x: foo / b: bar',... namespaces = {'x': 'http://codespeak.web/ns/test1',... 'b': 'http://codespeak.web/ns/test2'})>>> len (r)one>>> r [0]. day"{Http://codespeak.web/ns/test2ealogbar">>> r [0] .textual content'Textual content'