To Lecture Notes

IT 211 -- Mar 6, 2019

Review Exercises

1. Of the aggregate datatypes list, tuple, dict, and a user defined class, which are mutable and which are immutable? Ans:
   
   

   Datatype	Mutability
   list	Mutable
   tuple	Immutable
   dict	Mutable
   class	Mutable

   
   
2. What is the advantage of a dictionary instead of a list or tuple to represent an object?
   Ans: With a dictionary, one can look up information by key, which is usually easier to read than looking up by index.
3. What is the advantage of using a class over a dictionary to represent an object?
   Ans: With a class, the lookup is even easier to understand than it is for dictionaries. For a class: p.age, for a dictionary: p["age"].
4. What is the difference between a standalone method and an instance method?
   Ans: a standalone method is not called from an object, for example,
   

   print(n)
   

   An instance method is called from an object, for example,
   

   # The instance variable upper is called from the object s.
   u = s.upper( )
   

5. Write scripts to do the following with this cinderella.txt file:
   
   1. Convert entire file to upper case.
   2. Count the number of words in the file.
6. What is a constructor?
   Ans: A constructor is a method that creates an object, for example:
   

   n = int( )
   s = str( )
   p = Person("Alice", "F", 11)
   

7. What is a dunder method?
   Ans: A method with a double underscore prefix and double underscore suffix, for example:
   

   __init__  __str__
   

8. Look at the example class Pet files pet.py and test1.py, identify these items in each of the preceding classes and test files:
   
        Class Name   Instance Variable   Instance Method   Public Member
   
        Private Member  Dunder Method   Constructor   Local Variable 
   
        Standalone  Method   Parameter   Argument
   
   We worked on this Exercise in class today.  Try to identify these items yourself before looking at the answers.

Turtle Graphics

• Try out the turtle module. Use the statement
  

  import turtle

  at the top of your script
  
  1. Create a screen:
     

     s = turtle.Screen( )
     

  2. Create a turtle:
     

     t = turtle.Turtle( )
     

  3. Experiment with these Turtle instance methods:
     

     Instance Method	Parameter	Action
     backward	distance (int)	Move turtle backward
     color	color_name (str)	Change color of turtle pen
     forward	distance (str)	Move turtle forward
     heading		Return heading angle
     left	angle (int)	Turn turtle heading to left
     pendown		Put turtle pen down to write
     penup		Put turtle pen up to not write
     position		Return turtle position (x, y)
     right	angle (int)	Turn turtle heading to right

  4. Use for loops for repetitive drawing.
  5. Screen instance methods: title -- change screen window title, bye -- close the screen.
• Here are four Turtle Graphics sample scripts to try out.
• Here is the official Turtle documentation if you want more details.