code: def to_file(self, slug, folderpath=None, header=None, footer=None):
          
          if folderpath is None:
              if self.report_path is None:
                  self.err(
                      "Please set the report_path parameter or pass a path in arguments")
                  return
              folderpath = self.report_path
          else:
              self.report_path = folderpath
          html = self._get_header(header)
          if html is None or html == "":
              self.err(self.to_file, "Can not get html header")
          for report in self.reports:
              if "html" not in report:
                  self.err("No html for report " + report)
                  self.reports = self.report_engines = []
                  return
              html += report["html"]
          html += self._get_footer(footer)
          try:
              path = self._write_file(slug, folderpath, html)
              path = "file://" + path
          except Exception as e:
              self.err(e, self.to_file, "Can not save report to file")
              return
          self.reports = []
          self.report_engines = []
          if self.notebook is True:
              link = '<a href="' + path + '" target="_blank">' + path + '</a>'
              return display(HTML(link))
docs: Writes the html report to a file from the report stack