code: def _command(self, path=None):
          
          options = self._gegetate_args(self.options)
          options = [x for x in options]
          # print 'options', options
          if self.css:
              self._prepend_css(self.css)
  
          if '--xvfb' in options:
              options.remove('--xvfb')
              yield self.xvfb
              # auto servernum option to prevent failure on concurrent runs
              # https://bugs.launchpad.net/ubuntu/+source/xorg-server/+bug/348052
              yield '-a'
  
          yield self.wkhtmltoimage
  
          for argpart in options:
              if argpart:
                  yield argpart
  
          if self.cover and self.cover_first:
              yield 'cover'
              yield self.cover
  
          if self.toc:
              yield 'toc'
              for argpart in self._gegetate_args(self.toc):
                  if argpart:
                      yield argpart
  
          if self.cover and not self.cover_first:
              yield 'cover'
              yield self.cover
  
          # If the source is a string then we will pipe it into wkhtmltoimage
          # If the source is file-like then we will read from it and pipe it in
          if self.source.isString() or self.source.isFileObj():
              yield '-'
          else:
              if isinstance(self.source.source, basestring):
                  yield self.source.to_s()
              else:
                  for s in self.source.source:
                      yield s
  
          # If output_path evaluates to False append '-' to end of args
          # and wkhtmltoimage will pass generated IMG to stdout
          if path:
              yield path
          else:
              yield '-'
docs: Generator of all command parts
          :type options: object
          :return: