code: def _build_xpath_expr(attrs):
      
      # give class attribute as class_ because class is a python keyword
      if 'class_' in attrs:
          attrs['class'] = attrs.pop('class_')
  
      s = ["@{key}={val!r}".format(key=k, val=v) for k, v in attrs.items()]
      return '[{expr}]'.format(expr=' and '.join(s))
docs: Build an xpath expression to simulate bs4's ability to pass in kwargs to
      search for attributes when using the lxml parser.
  
      Parameters
      ----------
      attrs : dict
          A dict of HTML attributes. These are NOT checked for validity.
  
      Returns
      -------
      expr : unicode
          An XPath expression that checks for the given HTML attributes.