Introduction to Programming in Python
Turtle Graphics
Dr. Bill Young
Department of Computer Science University of Texas at Austin
Last updated: June 4, 2021 at 11:44
Turtle Graphics
Turtle graphics was first developed as part of the children’s
programming language Logo in the late 1960’s. It exemplifies OOP
extremely well. You will be using classes already defined for you.
Turtle Graphics
Turtles are just Python objects, so you can use any Python constructs in turtle programs:
selection, loops, recursion, etc.
Turtles are objects that move about on a screen (window).
Various methods allow you to direct the turtle’s movement.
The turtle’s tail can be up or down. When it is down, the turtle draws on the screen as it moves.
You can draw some pretty awesome images!
A Turtle Drawing
A Turtle Drawing
A Turtle Drawing: I Drew This One
A version of this picture was published in: William D. Young.
“Modeling and Verification of a Simple Real-Time Gate
Controller,” in Michael Hinchey and Jonathan Bowen, editors,
Applications of Formal Methods, Prentice-Hall Series in Computer
The Turtle’s Data
Like all Python classes, the turtle class defines data and methods.
The data (state) of the turtle consists of:
Position: denoted by its current x and y coordinates; the units are pixels.
Heading: denoted by an angle in degrees. East is 0 degrees.
north is 90 degrees; west is 180 degrees; south is 270 degrees.
Color: the color can be set to 2
24(∼ 16.8 million) colors.
Width: the width of the line drawn as the turtle moves (initially 2 pixels).
Down: a Boolean attribute indicating whether the turtle’s
tail is down.
Coordinate Grid
Turtle Methods
Many turtle methods are listing in your textbook (pages 81, 83) and online; Google “python turtle graphics.”
t = Turtle() create a new Turtle object and open its window t.home() move the turtle to (0, 0), pointing east
t.pendown() lower the tail (t.down() also works) t.penup() raise the tail (t.up() also works) t.pensize(k) set linewidth to k pixels
t.setheading(d) change heading to direction d t.left(d) turn left d degrees
t.right(d) turn right d degrees
t.speed(n) how fast the turtle moves (0 .. 10)
t.setx(n) set the turtle’s x coordinate, leave y unchanged
t.sety(n) set the turtle’s y coordinate, leave x unchanged
Turtle Methods
t.forward(n) move in the current direction n pixels t.backward(n) move in the reverse direction n pixels
t.goto(x, y) move to coordinates (x , y )
t.position() return the current position at a tuple (x, y) t.heading() return the current direction (angle)
t.isdown() return True if the pen is down
t.pencolor(r, g, b) change the color to the specified RGB value or named color
t.write(s, font) write a message to the screen (you can specify font
and size, e.g., “font=(’Arial’, 8, normal)”
Keeping it On Screen
Because the window goes away immediately after the program terminates, it may be hard to see the result unless you delay things. You can use t.done() for that.
t.done() make the screen persist until you close it
The turtle itself will appear on your screen as a small arrowhead.
You can decide whether to show or hide the turtle.
t.hideturtle() make the turtle invisible t.showturtle() make the turtle visible
t.isvisible() return True if the turtle is visible
A Turtle Function: Draw Square
i m p o r t t u r t l e
def d r a w S q u a r e ( ttl , x , y , l e n g t h ) :
""" D r a w s a s q u a r e u s i n g t u r t l e ttl , w i t h u p p e r l e f t c o r n e r at ( x , y ) , and s i d e of l e n g t h """
ttl . p e n u p () # r a i s e the pen
ttl . g o t o ( x , y ) # m o v e to s t a r t i n g p o s i t i o n ttl . s e t h e a d i n g (0) # p o i n t t u r t l e e a s t
ttl . p e n d o w n () # l o w e r the pen
for c o u n t in r a n g e(4) : # d r a w 4 s i d e s :
ttl . f o r w a r d ( l e n g t h ) # m o v e f o r w a r d l e n g t h ; ttl . r i g h t ( 9 0 ) # t u r n r i g h t 90 d e g r e e s
ttl . p e n u p () # r a i s e the pen
Bob = t u r t l e . T u r t l e () # our t u r t l e is n a m e d Bob Bob . s p e e d ( 1 0 ) # m a k e Bob c r a w l f a s t Bob . p e n s i z e (3) # l i n e w i d t h of 3 p i x e l s d r a w S q u a r e ( Bob , 0 , 0 , 100 ) # d r a w a s q u a r e at (0 ,0)
# w it h s i d e l e n g t h 100 t u r t l e . d o n e () # k e e p d r a w i n g s h o w i n g
What the Turtle Drew
Colors
I’m not sure this works on all versions of turtle graphics.
Colors are in the RGB system, using a triple: (R, G , B). Each element in the triple is an intensity from 0 to 255, indicating the contribution of R (red), G (green), and B (blue). For example:
black (0,0,0) red (255,0, 0) green (0, 255, 0)
blue (0, 0, 255) gray (127, 127, 127) white (255, 255, 255) burnt orange (255, 125, 25)
This is a nice website that allows you to find the RGB values for various colors: www.colorschemer.com/color-picker.
The named Python colors can be found here:
Color Wheel
Colors
Turtles have two “colormodes” and you’ll get an error if you try to do some things in the wrong mode. The modes are 1.0 and 255.
In mode 255, use triples of range 0 ≤ c ≤ 255. In mode 1, use triples (percentages) in range 0 . . . 1.
> > > t = T u r t l e ()
> > > t . p e n c o l o r (127 , 127 , 1 2 7 ) T r a c e b a c k ( m o s t r e c e n t c a l l l a s t ) :
F i l e " < stdin > " , l i n e 1 , in < module >
. . . .
r a i s e T u r t l e G r a p h i c s E r r o r ( " bad c o l o r s e q u e n c e : % s " % str ( c o l o r ) )
t u r t l e . T u r t l e G r a p h i c s E r r o r : bad c o l o r s e q u e n c e : (127 , 127 , 1 2 7 )
> > > t . p e n c o l o r (0.5 , 0.5 , 0 . 5 )
> > > t . s c r e e n . c o l o r m o d e ( 2 5 5 )
> > > p r i n t ( t . s c r e e n . c o l o r m o d e () ) 255
> > > t . p e n c o l o r (127 , 127 , 1 2 7 )
> > > t . s c r e e n . c o l o r m o d e (1)
Another Way
If you’re in colormode 255, you can also specify the color with a hex string value.
For example, the color Burnt Orange can be specified with the RGB decimal triple: (255, 125, 25).
You can also specify it with the hex string value: ’#FF7D19’
because 255 is hex (base 16) value FF, 125 is hex value 7D, and 25 is hex value 19.
> > > ttl . s c r e e n . c o l o r m o d e ( 2 5 5 )
> > > ttl . p e n c o l o r (255 , 125 , 25)
> > > p r i n t( ttl . p e n c o l o r () ) (255.0 , 125.0 , 2 5 . 0 )
> > > ttl . p e n c o l o r ( ’ # F F 7 D 1 9 ’ )
> > > p r i n t( ttl . p e n c o l o r () ) (255.0 , 125.0 , 2 5 . 0 )
Circles
You can draw circles, arcs, and dots using these functions:
t.circle(r, ext, step) draw a circle with radius r, ext (arc of circle drawn; 360 is entire circle), step (number of segments).
t.dot(d, color) draw a filled circle with diameter r and color Note: the circle is not centered at the starting point. If you want that you could write:
def c e n t e r e d C i r c l e ( ttl , r , x , y ) :
""" D r a w a c i r c l e w i t h r a d i u s r c e n t e r e d at ( x , y ) . """
ttl . up () # r a i s e the pen
a n g l e = ttl . h e a d i n g () # s a v e the c u r r e n t h e a d i n g ttl . s e t h e a d i n g (0) # set h e a d i n g e a s t
ttl . g o t o ( x , y - r ) # m o v e to b o t t o m of c i r c l e
ttl . d o w n () # pen d o w n
ttl . c i r c l e ( r ) # d r a w the c i r c l e
ttl . up () # pen up
Circles
def d r a w S o m e C i r c l e s ( ttl ) : ttl . s p e e d ( 1 0 )
ttl . p e n s i z e (3) # l i n e is 3 p i x e l s ttl . up ()
ttl . h o m e () # go to (0 , 0)
ttl . d o w n ()
ttl . p e n c o l o r ( ’ G r e e n ’ )
ttl . c i r c l e ( 2 5 ) # rad . 25 p i x e l s ttl . up ()
ttl . g o t o (0 , 0) ttl . p e n c o l o r ( ’ Red ’ ) ttl . d o w n ()
ttl . c i r c l e ( 5 0 , 1 8 0 ) # arc 180 deg . ttl . up ()
ttl . g o t o (0 , 0) ttl . p e n c o l o r ( ’ B l u e ’ ) ttl . d o w n ()
ttl . c i r c l e (75 ,360 ,8) # o c t o g o n ttl . up ()
Sam = t u r t l e . T u r t l e () d r a w S o m e C i r c l e s ( Sam )
More with Circles
def t a n g e n t C i r c l e s ( ttl ) :
""" P r i n t 10 t a n g e n t c i r c l e s . """
r = 10 # i n i t i a l r a d i u s n = 10 # c o u n t of c i r c l e s for i in r a n g e(1 , n + 1 , 1) :
ttl . c i r c l e ( r * i )
def c o n c e n t r i c C i r c l e s ( ttl ) :
""" P r i n t 10 c o n c e n t r i c c i r c l e s . """
r = 10 # i n i t i a l r a d i u s for i in r a n g e( 1 0 ) :
ttl . c i r c l e ( r * i ) ttl . up ()
ttl . s e t y (( r * i ) *( -1) ) ttl . d o w n ()
Ben = t u r t l e . T u r t l e () Ben . up () ; Ben . g o t o (0 , 1 5 0 ) Ben . d o w n () ; Ben . p e n c o l o r ( ’ B l u e ’ ) t a n g e n t C i r c l e s ( Ben )
Ben . up () ; Ben . g o t o (0 , -150)
Fill Areas
If you draw a closed region, you can fill it with a specified color:
t.fillcolor() sets the pen fill color
t.begin fill() call this before filling a shape t.end fill() call to no longer keep filling
t.filling() return True if filling, False otherwise
Drawing a Chessboard
def m a y b e F i l l S q u a r e ( ttl , x , y , lngth , fill , c o l o r ) :
""" B o o l e a n p a r a m e t e r f i l l s a y s w h e t h e r to f i l l . """
if f i l l :
ttl . f i l l c o l o r ( c o l o r ) ttl . b e g i n _ f i l l ()
d r a w S q u a r e ( ttl , x , y , l n g t h ) ttl . e n d _ f i l l ()
e l s e:
d r a w S q u a r e ( ttl , x , y , l n g t h )
def d r a w C h e s s b o a r d ( ttl , x , y , s q u a r e s i z e ) :
""" D r a w a t e a l and w h i t e c h e s s b o a r d . """
f i l l = T r u e
for j in r a n g e( 8 ) : for i in r a n g e( 8 ) :
x1 = x + i * s q u a r e s i z e y1 = y - j * s q u a r e s i z e
m a y b e F i l l S q u a r e ( ttl , x1 , y1 , s q u a r e s i z e , fill , ’ t e a l ’ )
f i l l = not f i l l f i l l = not f i l l
Our Chessboard
I don’t know why those weird lines are in there. They don’t show
up on the screen.
Sierpinski Curve
Some Complex Stuff: Sierpinski Curve
def o n e S i d e ( ttl , s , diag , l e v e l ) : if ( l e v e l == 0) :
r e t u r n e l s e:
o n e S i d e ( ttl , s , diag , l e v e l - 1 )
ttl . r i g h t ( 4 5 ) ; ttl . f o r w a r d ( d i a g ) ; ttl . r i g h t ( 4 5 ) o n e S i d e ( ttl , s , diag , l e v e l - 1 )
ttl . l e f t ( 9 0 ) ; ttl . f o r w a r d ( s ) ; ttl . l e f t ( 9 0 ) o n e S i d e ( ttl , s , diag , l e v e l - 1 )
ttl . r i g h t ( 4 5 ) ; ttl . f o r w a r d ( d i a g ) ; ttl . r i g h t ( 4 5 ) o n e S i d e ( ttl , s , diag , l e v e l - 1 )
def s i e r p i n s k i ( ttl , s , l e v e l ) : d i a g = s / m a t h . s q r t (2) for i in r a n g e(4) :
o n e S i d e ( ttl , s , diag , l e v e l ) ttl . r i g h t ( 4 5 )
ttl . f o r w a r d ( d i a g ) ttl . r i g h t ( 4 5 )
Some Complex Stuff: Fractal Triangles
Fractal Triangles
def d r a w O u t w a r d T r i a n g l e s ( ttl , s iz e ) : if s i z e < 10:
r e t u r n
for i in r a n g e( 3 ) :
ttl . f o r w a r d ( s i z e / 2 ) i n s e r t ( ttl , s i z e ) ttl . f o r w a r d ( s i z e / 2 ) ttl . r i g h t ( 120 )
def i n s e r t ( ttl , s i z e ) : ttl . l e f t ( 120 )
d r a w O u t w a r d T r i a n g l e s ( ttl , s i z e / 2 ) ttl . r i g h t ( 120 )
Ken = t u r t l e . T u r t l e () Ken . c o l o r ( " bl u e " )
d r a w O u t w a r d T r i a n g l e s ( Ken , 200 )
Saving Your Picture
Python saves your picture as a postscript file, but you can convert it. To save your picture as a jpeg, do the following:
f r o m PIL i m p o r t I m a g e
def s a v e _ a s _ j p g ( canvas , f i l e N a m e ) :
# s av e p o s t s c i p t i m a g e
c a n v a s . p o s t s c r i p t (f i l e = f i l e N a m e + ’ . eps ’ )
# use PIL to c o n v e r t to J P EG
img = I m a g e .o p e n( f i l e N a m e + ’ . eps ’ ) img . s a v e ( f i l e N a m e + ’ . j p e g ’ , ’ j p e g ’ )
< Y o u r d r a w i n g f u n c t i o n s >
ts = t u r t l e . g e t s c r e e n () tc = ts . g e t c a n v a s ()
# c r e a t e s a p o s t s c r i p t i m a g e f i l e
# s u b s t i t u t e y o u r own f i l e n a m e tc . p o s t s c r i p t (f i l e= " f i l e n a m e . eps " )
# c o n v e r t s to J P E G
s a v e _ a s _ j p g ( tc , " f i l e n a m e " )
Seychelles Flag
Drawing the Seychelles Flag
# T hi s d r a w s the f la g of the S e y c h e l l e s i s l a n d s :
i m p o r t t u r t l e
f r o m PIL i m p o r t I m a g e
def s a v e _ a s _ j p g ( canvas , f i l e N a m e ) :
# s am e as b e f o r e ...
def d r a w R e c t a n g l e ( ttl , x , y , width , h e i g h t ) :
""" D r a w a r e c t a n g l e of d i m e n s i o n s w i d t h and height , w i t h u p p e r l e f t c o r n e r at ( x , y ) . """
ttl . up () ttl . g o t o ( x , y ) ttl . s e t h e a d i n g (0) ttl . d o w n ()
for i in r a n g e(2) : ttl . f o r w a r d ( w i d t h ) ttl . r i g h t ( 9 0 ) ttl . f o r w a r d ( h e i g h t ) ttl . r i g h t ( 9 0 )
Drawing the Seychelles Flag
def d r a w T r i a n g l e ( ttl , x1 , y1 , x2 , y2 , x3 , y3 ) : ttl . p e n u p ()
ttl . g o t o ( x1 , y1 ) ttl . p e n d o w n () ttl . g o t o ( x2 , y2 ) ttl . g o t o ( x3 , y3 ) ttl . g o t o ( x1 , y1 ) ttl . p e n u p ()
def f i l l T r i a n g l e ( ttl , x1 , y1 , x2 , y2 , x3 , y3 , c o l o r ) :
# T hi s a s s u m e s c o l o r is g i v e n as a Hex s t r i n g v a l u e . ttl . f i l l c o l o r ( c o l o r )
ttl . b e g i n _ f i l l ()
d r a w T r i a n g l e ( ttl , x1 , y1 , x2 , y2 , x3 , y3 ) ttl . e n d _ f i l l ()
Drawing the Seychelles Flag
# set up the s c r e e n si z e ( in p i x e l s - 1 0 0 0 x 1 0 0 0 )
# set the s t a r t i n g p o i n t of the t u r t l e (0 , 0) t u r t l e . s e t u p (1500 , 1000 , 0 , 0)
m y B l u e = ’ # 0 0 3 8 8 2 ’ m y Y e l l o w = ’ # F C D 6 4 7 ’ m y R e d = ’ # D 1 2 4 2 1 ’ m y G r e e n = ’ # 0 0 7 3 3 6 ’ m y W h i t e = ’ # F F F F F F ’ Joe = t u r t l e . T u r t l e () Joe . s c r e e n . c o l o r m o d e ( 2 5 5 )
d r a w R e c t a n g l e ( Joe , 0 , 300 , 600 , 300 ) Joe . g o t o (0 , 0)
# d ra w b l u e t r i a n g l e
f i l l T r i a n g l e ( Joe , 0 , 0 , 0 , 300 , 200 , 300 , m y B l u e )
# d ra w y e l l o w t r i a n g l e
f i l l T r i a n g l e ( Joe , 0 , 0 , 200 , 300 , 400 , 300 , m y Y e l l o w )
# d ra w red t r i a n g l e
f i l l T r i a n g l e ( Joe , 0 , 0 , 400 , 300 , 600 , 300 , m y R e d )
# d ra w w h i t e t r i a n g l e
f i l l T r i a n g l e ( Joe , 0 , 0 , 600 , 300 , 600 , 150 , m y W h i t e )
# d ra w g r e e n t r i a n g l e
Drawing the Seychelles Flag
Joe . h i d e t u r t l e ()
ts = t u r t l e . g e t s c r e e n () tc = ts . g e t c a n v a s ()
# c r e a t e s a p o s t s c r i p t i m a g e f i l e
# s u b s t i t u t e y o u r own f i l e n a m e
tc . p o s t s c r i p t (f i l e= " S e y c h e l l e s F l a g . eps " )
# c o n v e r t s to J P E G
s a v e _ a s _ j p g ( tc , " S e y c h e l l e s F l a g " ) t u r t l e . d o n e ()
Some Sample Projects
Write Turtle graphics functions that will do the following:
1
draw a cube;
2
draw a regular polygon with k sides and radius r (distance from center to one of the vertices);
3
draw m concentric circles, varying the color as you go outward;
4
draw the flag of some country;
5
