'Turns turtle animation on/off and set delay for update drawings.
Optional arguments:
n -- nonnegative  integer
delay -- nonnegative  integer
If n is given, only each n-th regular screen update is really performed.
(Can be used to accelerate the drawing of complex graphics.)
Second arguments sets delay value (see RawTurtle.delay())
Example (for a Turtle instance named turtle):
>>> turtle.tracer(8, 25)
>>> dist = 2
>>> for i in range(200):
turtle.fd(dist)
turtle.rt(90)
dist += 2'

def tracer(self, flag=None, delay=None):

    return self.screen.tracer(flag, delay)
