parameters: (self, picname=None)
docstring: Set background image or return name of current backgroundimage.
  
          Optional argument:
          picname -- a string, name of a gif-file or "nopic".
  
          If picname is a filename, set the corresponding image as background.
          If picname is "nopic", delete backgroundimage, if present.
          If picname is None, return the filename of the current backgroundimage.
  
          Example (for a TurtleScreen instance named screen):
          >>> screen.bgpic()
          'nopic'
          >>> screen.bgpic("landscape.gif")
          >>> screen.bgpic()
          'landscape.gif'
docstring_summary: Set background image or return name of current backgroundimage.
docstring_tokens: Set background image or return name of current backgroundimage .
function: def bgpic(self, picname=None):
          """Set background image or return name of current backgroundimage.
  
          Optional argument:
          picname -- a string, name of a gif-file or "nopic".
  
          If picname is a filename, set the corresponding image as background.
          If picname is "nopic", delete backgroundimage, if present.
          If picname is None, return the filename of the current backgroundimage.
  
          Example (for a TurtleScreen instance named screen):
          >>> screen.bgpic()
          'nopic'
          >>> screen.bgpic("landscape.gif")
          >>> screen.bgpic()
          'landscape.gif'
          """
          if picname is None:
              return self._bgpicname
          if picname not in self._bgpics:
              self._bgpics[picname] = self._image(picname)
          self._setbgpic(self._bgpic, self._bgpics[picname])
          self._bgpicname = picname
function_tokens: def bgpic ( self , picname = None ) : if picname is None : return self . _bgpicname if picname not in self . _bgpics : self . _bgpics [ picname ] = self . _image ( picname ) self . _setbgpic ( self . _bgpic , self . _bgpics [ picname ] ) self . _bgpicname = picname