def extract_content(self, selector, attr, default):
		"""
		Method for performing the content extraction for the given XPath expression.

		The XPath selector expression can be used to extract content \
		from the element tree corresponding to the fetched web page.

		If the selector is "url", the URL of the current web page is returned.
		Otherwise, the selector expression is used to extract content. The particular \
		attribute to be extracted ("text", "href", etc.) is specified in the method \
		arguments, and this is used to extract the required content. If the content \
		extracted is a link (from an attr value of "href" or "src"), the URL is parsed \
		to convert the relative path into an absolute path.

		If the selector does not fetch any content, the default value is returned. \
		If no default value is specified, an exception is raised.

		:param selector: The XPath expression
		:param attr: The attribute to be extracted from the selected tag
		:param default: The default value to be used if the selector does not return any data
		:return: The extracted content

		"""
		try:
			if selector == "url":
				return self.url
			if attr == "text":
				tag = self.tree.xpath(selector)[0]
				content = " ".join([make_ascii(x).strip() for x in tag.itertext()])
				content = content.replace("\n", " ").strip()
			else:
				content = self.tree.xpath(selector)[0].get(attr)
				if attr in ["href", "src"]:
					content = urljoin(self.url, content)
			return content
		except __HOLE__:
			if default is not "":
				return default
			raise Exception("There is no content for the selector " + selector)
		except XPathError:
			raise Exception("Invalid XPath selector " + selector)
dataset/ETHPy150Open AlexMathew/scrapple/scrapple/selectors/xpath.py/XpathSelector.extract_content