1. Introduction to Programming: Module #2 Python, Trinket, and Turtle Graphics
Lois Delcambre

2. First … a comment about blockly
Most programming languages – including those used by professionals – have the following constructs:
function definition
repeat loop – repeat code a specific number of times
repeat until – repeat code until some condition is True
if statement – to ask questions
else statement – second part of an if statement
You are already a programmer!

3. Plan for Today Introduce Python at trinket.io
Introduce the turtle module
Define functions in Python
Compare blockly and Python
Write your own Python programs. Write your own trinkets.

4. trinket – see next few slides for images of these steps
go to trinket.io
click on “Learn” tab – at the top right
click on “Start Learning” for Python with Turtles
(in Free Lessons)
click on “Meet Tina”
(one lesson; the lessons are listed on the left side)

5. click on “Learn” tab – at the top right
go to trinket.io
click on “Learn” tab – at the top right

6. Click on Start Learning!

7. To see the Table of Contents, click here:

8. With Table of Contents expanded, you can see the lessons here:

9. We’ll start with “Meet Tina”

10. A Python program

11. The button to push – to run the program

12. The output from this program

13. If you want to reset the program in a lesson …
Click on this menu
Then choose Reset
Sometimes, you need to click on another lesson and then back to this one after you reset.

14. Plan for Today Introduce Python at trinket.io
Introduce the turtle module
Define functions in Python
Compare blockly and Python
Write your own Python programs. Write your own trinkets.

15. Meet Tina program import turtle tina = turtle.Turtle()
tina.shape('turtle')
tina.penup()
tina.forward(20)
tina.write("Why, hello there!")
tina.backward(20)

16. Meet Tina program – explained (1)
import allows you to
use all of the functions
and methods written
in the module.
Here we import the turtle module.
import turtle
tina = turtle.Turtle()
tina.shape('turtle')
tina.penup()
tina.forward(20)
tina.write("Why, hello there!")
tina.backward(20)

17. Meet Tina program – explained (2)
the Turtle method in the
turtle module creates a new turtle.
This new turtle becomes
associated with the name (that the programmer chose)
tina.
import turtle
tina = turtle.Turtle()
tina.shape('turtle')
tina.penup()
tina.forward(20)
tina.write("Why, hello there!")
tina.backward(20)

18. Meet Tina program – explained (3)
To use a method
in the turtle module:
name of the module (turtle)
followed by a dot (.)
and then
the method name.
(Turtle).
import turtle
tina = turtle.Turtle()
tina.shape('turtle')
tina.penup()
tina.forward(20)
tina.write("Why, hello there!")
tina.backward(20)

19. Meet Tina program – explained (4)
For a turtle object (named tina), we can invoke methods (from the turtle module).
Use:
the name of the turtle (tina)
followed by a dot (.)
and the method name (shape, penup, forward, write, backward).
import turtle
tina = turtle.Turtle()
tina.shape('turtle')
tina.penup()
tina.forward(20)
tina.write("Why, hello there!")
tina.backward(20)

20. Parameters for functions/methods
Sometimes (in real life), we don’t need parameters: “I’ll take the blue plate special.” That’s it. A nice lunch will be delivered.
Sometimes (in real life), we supply parameters: “The cheeseburger meal, please.” What kind of cheese? Swiss What size french fries? medium What size soft drink? large “Swiss”, “medium”, and “large” are given to the chef – so they can prepare your lunch.

21. Parameters for functions/methods Some functions/methods need them; some don’t
the forward method has one parameter – how far to go forward.
the penup method has no parameters. It simply puts the pen up.
import turtle
tina = turtle.Turtle()
tina.shape('turtle')
tina.penup()
tina.forward(20)
tina.write("Why, hello there!")
tina.backward(20)

22. Meet Tina program – explained (5)
Every time you
invoke a function
or method, you
put the name of the function/method and then you put
the parameters to that function/method in
parentheses.
If you have no parameters,
you put open/close parentheses – with nothing in between.
import turtle
tina = turtle.Turtle()
tina.shape('turtle')
tina.penup()
tina.forward(20)
tina.write("Why, hello there!")
tina.backward(20)

23. Coordinate space for turtle turtle has a “heading” – starts out East (to the right), as shown
200
-200

24. Class work
On your own
the Moving lesson

25. Saying Hello program explained (1)
input is a function
that is part of Python.
Every program can use
it.
See: no “tina” in front of the name of the function.
We just put the name of the
function and then
the parameter(s).
import turtle
tina = turtle.Turtle()
tina.shape('turtle')
your_name = input("What's your name?")
tina.penup()
tina.forward(20)
tina.write("Why, hello, " + your_name + "!")
tina.backward(20)

26. functions some functions are built-in to Python
input: allow the user to enter text,
abs: returns the absolute value of the parameter
some functions are provided in modules
math module: gcd, factorial, cos, sin, tan, …
functions often have one or more parameters
functions typically return some sort of value
input – hands over the text typed by the user
gcd – hands over the number that is the greatest common divisor of the two parameters

27. functions vs. methods
In Python and in existing modules, some things are defined as functions; others are defined as methods.
The only difference is that a method needs to be applied to an object (of the right type). The object is kind of like an “automatic” parameter.

28. methods tina is a turtle object in the Meet Tina program, for example
thus, we can invoke all turtle methods for tina
tina.forward
tina.penup
etc.

29. Saying Hello program explained (2)
The parameter to
the input function is the text that is displayed to the user.
This program will
then wait for the
user to type
in their response (and
hit enter).
import turtle
tina = turtle.Turtle()
tina.shape('turtle')
your_name = input("What's your name?")
tina.penup()
tina.forward(20)
tina.write("Why, hello, " + your_name + "!")
tina.backward(20)

30. Saying Hello program explained (3)
Whenever you have
some text in your program, you have
to put quotes around it.
In Python, single quotes (‘word’)
or double quotes (“word”)
will work.
import turtle
tina = turtle.Turtle()
tina.shape('turtle')
your_name = input("What's your name?")
tina.penup()
tina.forward(20)
tina.write("Why, hello, " + your_name + "!")
tina.backward(20)

31. Saying Hello program explained (4)
What does the equal sign do?
import turtle
tina = turtle.Turtle()
tina.shape('turtle')
your_name = input("What's your name?")
tina.penup()
tina.forward(20)
tina.write("Why, hello, " + your_name + "!")
tina.backward(20)

32. Assignment statements in Python (1)
tina = turtle.Turtle()
This is an assignment statement.
tina is a variable name, chosen by the programmer.
The variable size “gets” or becomes associated with whatever is returned by the right side of the assignment statement.
In this case, the variable tina gets a turtle object because the Turtle method in Python returns a turtle object.

33. Assignment statements in Python (2)
An assignment
statement introduces
a new name (if it’s
the first time you’ve
used that name).
Here, the variable
name (tina) gets a new turtle object!
import turtle
tina = turtle.Turtle()
tina.shape('turtle')
your_name = input("What's your name?")
tina.penup()
tina.forward(20)
tina.write("Why, hello, " + your_name + "!")
tina.backward(20)

34. Assignment statements in Python (3)
Once you have a name (with its value),
you can use that name
(again and again) to
refer to that value.
Here, we invoke a
number of methods
that are appropriate for a turtle object using the name
tina – a turtle object.
import turtle
tina = turtle.Turtle()
tina.shape('turtle')
your_name = input("What's your name?")
tina.penup()
tina.forward(20)
tina.write("Why, hello, " + your_name + "!")
tina.backward(20)

35. Assignment statements in Python (4)
Here, the variable
(your_name) gets
the value of whatever is
returned from the
input function.
The input function
will return whatever
the user types in as a string.
import turtle
tina = turtle.Turtle()
tina.shape('turtle')
your_name = input("What's your name?")
tina.penup()
tina.forward(20)
tina.write("Why, hello, " + your_name + "!")
tina.backward(20)

36. Assignment statements in Python (5)
Now that the
variable (your_name)
has a value, we
can use that variable
whenever we want
to used the value.
import turtle
tina = turtle.Turtle()
tina.shape('turtle')
your_name = input("What's your name?")
tina.penup()
tina.forward(20)
tina.write("Why, hello, " + your_name + "!")
tina.backward(20)

37. Saying Hello program explained (5)
The plus symbol (+) is used to concatenate
strings (text).
Here – the write
method (invoked for
the turtle object with the name tina)
will write out
Why, hello, <value of your_name variable>!
import turtle
tina = turtle.Turtle()
tina.shape('turtle')
your_name = input("What's your name?")
tina.penup()
tina.forward(20)
tina.write("Why, hello, " + your_name + "!")
tina.backward(20)

38. Class work
On your own:
Color lesson
Tina’s Pen lesson (Draw 2 parallel sides)
Tina’s grid lesson (Draw box at bottom left of screen)
Going in Circles lesson
We’ll cover Repeating with Loops and Lists tomorrow
Skip: Lists of numbers, Loops of Lists, Changing Colors lessons
Turtles are Objects lesson
Tina and Tommy’s Colors lesson

39. Plan for Today Introduce Python at trinket.io
Introduce the turtle module
Define functions in Python
Compare blockly and Python
Write your own Python programs. Write your own trinkets.

40. the Functions are recipes! lesson – explained (1)
import turtle
tina=turtle.Turtle()
tina.shape('turtle')
tina.color('purple')
def triangle():
tina.left(60)
tina.forward(30)
tina.left(120)
triangle()

41. the Functions are recipes
the Functions are recipes! lesson – explained (2) def to define a function
import turtle
tina=turtle.Turtle()
tina.shape('turtle')
tina.color('purple')
def triangle():
tina.left(60)
tina.forward(30)
tina.left(120)
triangle()
Function definition here.
The name of the function here.

42. the Functions are recipes
the Functions are recipes! lesson – explained (3) def to define a function
import turtle
tina=turtle.Turtle()
tina.shape('turtle')
tina.color('purple')
def triangle():
tina.left(60)
tina.forward(30)
tina.left(120)
triangle()
Function definition here.
The Python interpreter processes this function definition;
remembers the name of the function; it will run the
code inside the function if the function is ever invoked.

43. the Functions are recipes! lesson – explained (4) function invocation
import turtle
tina=turtle.Turtle()
tina.shape('turtle')
tina.color('purple')
def triangle():
tina.left(60)
tina.forward(30)
tina.left(120)
triangle()
Function definition here.
The Python interpreter processes this function definition;
remembers the name of the function; it will run the
code inside the function if the function is ever invoked.
Function invocation here. Invokes the function named triangle.

44. the Functions are recipes
the Functions are recipes! lesson – explained (5) this function (triangle) doesn’t have any parameters
import turtle
tina=turtle.Turtle()
tina.shape('turtle')
tina.color('purple')
def triangle():
tina.left(60)
tina.forward(30)
tina.left(120)
triangle()
No parameters listed here in the function definition.
No parameter values provided here when the function is invoked.

45. the Functions are recipes
the Functions are recipes! lesson – explained (6) the code block inside a function definition
import turtle
tina=turtle.Turtle()
tina.shape('turtle')
tina.color('purple')
def triangle():
tina.left(60)
tina.forward(30)
tina.left(120)
triangle()
Code block
begins with a : on the previous line
Code inside the code block
must be indented
The code block ends when code is unindented.
The unindented line is NOT part of the code block in this function.

46. Plan for Today Introduce Python at trinket.io
Introduce the turtle module
Define functions in Python
Compare blockly and Python
Write your own Python programs. Write your own trinkets.

47. blockly vs. Python Moving program
They both have one command after the other.
You can have blank lines in Python – anywhere.

48. blockly vs. Python turtle module
Moving program
“move forward”
repeated in program
(zombie takes one
step at a time)
“forward” method in the turtle module
takes one parameter:
the number of pixels to move forward.
There is also a “backward” method.

49. blockly vs. Python turtle module (cont.)
Moving program
“right” method in the turtle module
takes one parameter:
the number of degrees to turn.
There is also a “left” method.
Parameter can be negative/positive.
“turn”
can turn left or right

50. blockly vs. Python function definition import turtle
tina=turtle.Turtle()
tina.shape('turtle')
tina.color('purple')
def triangle():
tina.left(60)
tina.forward(30)
tina.left(120)
triangle()
function
definition
Functions are Recipes! program

51. blockly vs. Python function name import turtle tina=turtle.Turtle()
tina.shape('turtle')
tina.color('purple')
def triangle():
tina.left(60)
tina.forward(30)
tina.left(120)
triangle()
function
name
Functions are Recipes! program

52. blockly vs. Python function invocation import turtle
tina=turtle.Turtle()
tina.shape('turtle')
tina.color('purple')
def triangle():
tina.left(60)
tina.forward(30)
tina.left(120)
triangle()
function
invocation
Functions are Recipes! program

53. Class Work Work on your own: Functions are recipes! lesson
Make 5 cakes lesson

54. Plan for Today Introduce Python at trinket.io
Introduce the turtle module
Define functions in Python
Compare blockly and Python
Write your own Python programs. Write your own trinkets.

55. punctuation
Can you read this?
Mary is my sister she’s taller than me she. . has blonde hair she’s younger than I am

56. punctuation (cont.)
Mary is my sister she’s taller than me she. . has blonde hair she’s younger than I am
A computer would have trouble. It uses rules to decide where commands end. It would find these “sentences”:
Mary is my sister she’s taller than me she.
a sentence .
empty sentence
has blonde hair she’s younger than I am
not (yet) a sentence because we haven’t encountered a period

57. In Python, some punctuation must be precise (try this)
All statements lined up
on left margin (except for block – which is indented).
block begins with a : then all statements indented – the same amount. block ends with unindented line.

58. In Python, other punctuation is flexible (try this)
You can have blank lines – anywhere you want them.
You can put 1 or more spaces in between parameters and before and after the “=“ sign. (or not)

59. Write your own Python programs – write trinkets see next few slides to see what this looks like
Make sure you’re logged in to trinket
go to: home
click on tab – with your userid; choose My Trinkets
click on “new trinket” in the upper right corner
choose Python (not Python 3)
When you’re creating your code for this new trinket:
change “Untitled” to the name you want for this program
type your code in; run it when you want to; save often

60. How to write your own trinkets (Python programs)
Make sure you’re logged in to trinket
Right click on your user name (mine is lmd_0977)
Choose the one that says My Trinkets

61. Click on the “New Trinket” button
Then … choose Python

62. type your Python program here

63. push this button to run your program
see output here \

64. Programming Challenge
Write a new trinket that draws a rectangular rainbow.
Colors are: red, orange, yellow, green, blue, indigo and violet.
Goal: define at least one function
Advanced goal: define at least one useful parameter in one of your functions