code: def load(self, url, offset, length):
          
          headers = {}
          if offset != 0 or length != -1:
              headers['Range'] = BlockLoader._make_range_header(offset, length)
  
          if self.cookie_maker:
              if isinstance(self.cookie_maker, six.string_types):
                  headers['Cookie'] = self.cookie_maker
              else:
                  headers['Cookie'] = self.cookie_maker.make()
  
          if not self.session:
              self.session = requests.Session()
  
          r = self.session.get(url, headers=headers, stream=True)
          r.raise_for_status()
          return r.raw
docs: Load a file-like reader over http using range requests
          and an optional cookie created via a cookie_maker