code: def get_template_file(self):
          
          if os.path.exists(os.path.join(self.theme_dir, 'base.html')):
              return os.path.join(self.theme_dir, 'base.html')
          default_dir = os.path.join(THEMES_DIR, 'default')
          if not os.path.exists(os.path.join(default_dir, 'base.html')):
              raise IOError(u"Cannot find base.html in default theme")
          return os.path.join(default_dir, 'base.html')
docs: Retrieves Jinja2 template file path.