code: def load(self, *page_numbers):
          
          self.tree = self.get_tree(*_flatten(page_numbers))
          self.pq = self.get_pyquery(self.tree)
docs: Load etree and pyquery object for entire document, or given page
          numbers (ints or lists). After this is called, objects are
          available at pdf.tree and pdf.pq.
  
          >>> pdf.load()
          >>> pdf.tree
          <lxml.etree._ElementTree object at ...>
          >>> pdf.pq('LTPage')
          [<LTPage>, <LTPage>]
          >>> pdf.load(1)
          >>> pdf.pq('LTPage')
          [<LTPage>]
          >>> pdf.load(0, 1)
          >>> pdf.pq('LTPage')
          [<LTPage>, <LTPage>]