docs: def get_shape(kind='line',x=None,y=None,x0=None,y0=None,x1=None,y1=None,span=0,color='red',dash='solid',width=1,
  				fillcolor=None,fill=False,opacity=1,xref='x',yref='y'):
  	"""
  	Returns a plotly shape
  
  	Parameters:
  	-----------
  		kind : string
  			Shape kind
  				line
  				rect
  				circle
  		x : float
  			x values for the shape.
  			This assumes x0=x1
  		x0 : float
  			x0 value for the shape
  		x1 : float
  			x1 value for the shape
  		y : float
  			y values for the shape.
  			This assumes y0=y1
  		y0 : float
  			y0 value for the shape
  		y1 : float
  			y1 value for the shape
  		color : string
  			color for shape line
  		dash : string
  			line style
  				solid
  				dash
  				dashdot
  				dot
  		width : int
  			line width
  		fillcolor : string
  			shape fill color
  		fill : bool
  			If True then fill shape
  			If not fillcolor then the
  			line color will be used
  		opacity : float [0,1]
  			opacity of the fill
  		xref : string
  			Sets the x coordinate system
  			which this object refers to
  				'x'
  				'paper'
  				'x2' etc
  		yref : string
  			Sets the y coordinate system
  			which this object refers to
  				'y'
  				'paper'
  				'y2' etc
  	"""
  	if x1 is None:
  		if x0 is None:
  			if x is None:
  				xref='paper'
  				x0=0
  				x1=1
  			else:
  				x0=x1=x
  		else:
  			x1=x0
  	else:
  		x
  	if y1 is None:
  		if y0 is None:
  			if y is None:
  				yref='paper'
  				y0=0
  				y1=1
  			else:
  				y0=y1=y
  		else:
  			y1=y0
  
  	shape = {	'x0':x0,
  				'y0':y0,
  				'x1':x1,
  				'y1':y1,
  				'line' : {
  					'color':normalize(color),
  					'width':width,
  					'dash':dash
  					},
  				'xref':xref,
  				'yref':yref
  				}
  
  	if kind=='line':
  		shape['type']='line'
  
  	elif kind=='circle':
  		shape['type']='circle'
  
  	elif kind=='rect':
  		shape['type']='rect'
  	else:
  		raise Exception("Invalid or unkown shape type : {0}".format(kind))
  
  	if (fill or fillcolor) and kind!='line':
  		fillcolor = color if not fillcolor else fillcolor
  		fillcolor=to_rgba(normalize(fillcolor),opacity)
  		shape['fillcolor']=fillcolor
  
  	return shape