1. EECS 110: Lec 15: Classes and Objects (2)
Aleksandar Kuzmanovic
Northwestern University

2. Fri., 5/28: recitation (LR5) Tue., 6/1: recitation, W. lab
EECS 110 important dates
Projects
Projects
Final!
Fri., 5/21: online
Fri., 5/28: recitation (LR5) Tue., 6/1: recitation, W. lab
Wed., 5/26: rev. for final
Wed., 6/2, final
Mon., 5/24: class

3. (1) A class is a type of variable.
Classes & Objects
An object-oriented programming language allows you to build your own customized types of variables.
(1) A class is a type of variable.
(2) An object is one such variable.
There will typically be MANY objects of a single class.

4. Objects An object is a data structure (like a list), except
(1) Its data elements have names chosen by the programmer.
(2) Data elements are chosen & organized by the programmer
(3) An object can have behaviors built-in by the programmer.

5. usually called "methods" instead of functions
Objects
An object is a data structure (like a list), except
(1) Its data elements have names chosen by the programmer.
(2) Data elements are chosen & organized by the programmer
(3) An object can have behaviors built-in by the programmer.
usually called "methods" instead of functions

6. The Date class class Date: """ a blueprint (class) for objects
that represent calendar days
"""
def __init__( self, mo, dy, yr ):
""" the Date constructor """
self.month = mo
self.day = dy
self.year = yr
def __repr__( self ):
""" used for printing Dates """
s = "%02d/%02d/%04d" % (self.month, self.day, self.year)
return s
The Date class

7. EECS 110 Today Connect Four | | | | | | | | | | | |X| | | |
| |X| |X|O| | |
|X|O|O|O|X|O| |
X to move.
Is there a way to win?

8. Aargh! Python has no Connect-four datatype… | | | | | | | |
| | | |X| | | |
| |X| |X|O| | |
|X|O|O|O|X| |O|
… but we can correct that!

9. Designing classes 1) What data? (Data Members)
Not limited to 7x6!
2) What are objects' crucial capabilities? (Methods)

10. Designing classes What data? (Data Members)
- height, width
- Where the chips are
- Whose turn it is
- Winning condition
- End condition (number of chips played)
Not limited to 7x6!
2) What are objects' crucial capabilities? (Methods)

11. Designing classes What data? (Data Members)
- height, width
- Where the chips are
- Whose turn it is
- Winning condition
- End condition (number of chips played)
Not limited to 7x6!
2) What are objects' crucial capabilities? (Methods)
creates a new object
check for win
print
get the next move/switch turn
check for full board

12. Connect Four: the object b
int
str
str
str
str
list
width
Board b
data
int
str
str
str
str
height
str
str
str
str
data
What is the name of the method that will construct this data?

13. Connect Four: the object b
int
str
str
str
str
list
width
Board b
data
int
str
str
str
str
height
str
str
str
str
data
What is the name of the method that will construct this data?
__init__(…)

14. Connect Four: constructor
class Board:
""" a datatype representing a C4 board
with an arbitrary number of rows and cols
"""
def __init__( self, width, height ):
""" the constructor for objects of type Board """
self.width = width
self.height = height
self.data = [] # this will be the board
for row in range( height ): # 6
boardRow = []
for col in range( width ): # 7
boardRow += [' '] # add a space to this row
self.data += [boardRow]

15. Connect Four: the object b
int
str
str
str
str
list
width
Board b
data
int
str
str
str
str
height
str
str
str
str
| | | | | | | |
| | | |X| | | |
| |X| |X|O| | |
|X|O|O|O|X| |O|
What is the name of the method that will print this data?

16. Connect Four: __repr__
def __repr__(self):
""" this method returns a string representation
for an object of type Board
"""
s = ''
for row in range( self.height ):
s += '|'
for col in range( self.width ):
s += self.data[row][col] + '|'
s += '\n'
return s
which row is row 0, row 1, and so on?
To remove?
To add?

17. Connect Four: __repr__
def __repr__(self):
""" this method returns a string representation
for an object of type Board
"""
s = ''
for row in range( self.height ):
s += '|'
for col in range( self.width ):
s += self.data[row][col] + '|'
s += '\n‘
s += '--'*self.width + '-\n‘
s += ' ' + str(col%10)
s += '\n'
return s
which row is row 0, row 1, and so on?

18. Step through this mystery method.
"Quiz"
class Board {
def mystery(self, col, ox):
for row in range( self.height ):
if self.data[row][col] != ' ':
self.data[row-1][col] = ox
self.data[self.height-1][col] = ox
def allowsMove(self, col): }
a C4 board
col #
'X' or 'O'
Step through this mystery method.
What is each line doing?
What's going wrong?
Write allowsMove to return True if col is a valid move; False otherwise.

19. Step through this mystery method.
"Quiz"
class Board {
def mystery(self, col, ox):
for row in range( self.height ):
if self.data[row][col] != ' ':
self.data[row-1][col] = ox
self.data[self.height-1][col] = ox
# Adds ox at the top of a column
# But at the same time overwrites the existing
# elements in the column…
# Does not check if it is possible to write in a column…
def allowsMove(self, col): }
a C4 board
col #
'X' or 'O'
Step through this mystery method.
What is each line doing?
What's going wrong?
Write allowsMove to return True if col is a valid move; False otherwise.

20. Step through this mystery method.
"Quiz"
class Board {
def mystery1(self, col, ox):
if allowsMove(col):
for row in range( self.height ):
if self.data[row][col] != ' ':
self.data[row-1][col] = ox
return
self.data[self.height-1][col] = ox
def allowsMove(self, col): }
a C4 board
col #
'X' or 'O'
Step through this mystery method.
What is each line doing?
What's going wrong?
Write allowsMove to return True if col is a valid move; False otherwise.

21. Step through this mystery method.
"Quiz"
class Board {
def mystery1(self, col, ox):
if allowsMove(col):
for row in range( self.height ):
if self.data[row][col] != ' ':
self.data[row-1][col] = ox
return
self.data[self.height-1][col] = ox
def allowsMove(self, col):
if 0 <= col < self.width:
return self.data[0][col] == ' ' }
a C4 board
col #
'X' or 'O'
Step through this mystery method.
What is each line doing?
What's going wrong?
Write allowsMove to return True if col is a valid move; False otherwise.

22. C4 Board class: methods Which of these will require the most thought?
the “constructor”
__init__( self, width, height )
checks if allowed
allowsMove( self, col )
places a checker
addMove( self, col, ox )
removes a checker
delMove( self, col )
__repr__( self )
outputs a string
isFull( self )
checks if any space is left
winsFor( self, ox )
checks if a player has won
hostGame( self )
play!
Which of these will require the most thought?

23. winsFor( self, ox ) b
b.winsFor( 'X' )
or 'O' X O
Thoughts?

24. winsFor( self, ox ) b Thoughts? X O def winsFor(self, ox):
# check for horizontal wins
for row in range(0,self.height):
for col in range(0,self.width-3):
if self.data[row][col] == ox and \
self.data[row][col+1] == ox and \
self.data[row][col+2] == ox and \
self.data[row][col+3] == ox:
return True
# check for vertical wins X O
Thoughts?

25. The Player class (Extra credit)
Details
Player
pForX
(data and methods)
What data and methods are needed to
construct and implement a Player object?

26. Player Picture of a Player object DATA 3 'X' 'LEFT' METHODS stringox
string
tbt
int
ply
Player
pForX
checker, O or X
tiebreakType
__init__(self, ox, tbt, ply)
__repr__(self)
oppCh(self)
METHODS
scoreBoard(self, b)
scoresFor(self, b)
tiebreakMove(self, scores)
nextMove(self, b)

27. scoreBoard ‘X’ ‘O’ Assigns a score to any board, b A simple system:
100.0
50.0
0.0
for a win
for anything else
for a loss
Score for
Score for
Score for
Score for

28. scoreBoard ‘X’ ‘O’ Assigns a score to any board, b A simple system:
100.0
50.0
0.0
for a win
for anything else
for a loss
Score for
100.0
Score for
Score for
0.0
Score for

29. scoreBoard ‘X’ ‘O’ Assigns a score to any board, b A simple system:
100.0
50.0
0.0
for a win
for anything else
for a loss
Score for
100.0
Score for
50.0
Score for
0.0
Score for
50.0

30. What class is this method in?
scoreBoard
Assigns a score to any board, b
A simple system:
100.0
50.0
0.0
for a win
for anything else
for a loss
Implementation ideas…
scoreBoard(self, b)
What methods that already exist will come in handy?
This doesn't seem to be looking very far ahead !
How can there be no 'X' or 'O' input?
What class is this method in?

31. Looking further ahead…
scoreBoard looks ahead 0 moves
0-ply
If you look one move ahead, how many possibilities are there to consider?
A 1-ply lookahead player will "see" an impending victory.
to move…
1-ply
score

32. Looking further ahead…
scoreBoard looks ahead 0 moves
0-ply
If you look one move ahead, how many possibilities are there to consider?
A 1-ply lookahead player will "see" an impending victory.
to move…
1-ply
score -1 50 50 50
100 50 50

33. Looking further ahead…
scoreBoard looks ahead 0 moves
0-ply
If you look one move ahead, how many possibilities are there to consider?
A 2-ply lookahead player will also "see" an opponent's impending victory.
to move…
2-ply -1 50
score

34. Looking further ahead…
scoreBoard looks ahead 0 moves
0-ply
If you look one move ahead, how many possibilities are there to consider?
1-ply
2-ply
scoresFor( self, b ) returns a LIST of scores, one for each column you can choose to move next…

35. Example 1-ply and 2-ply lookahead scores
It is O’s move. What scores does a 1-ply lookahead for O assign to each move?
|O| | | | | | |
|X| | | |O| |X|
|O| | | |X|O|X|
|X| | | |O|O|X|
|X| |X| |X|O|O|
|X| |O|O|O|X|X|
col 0
col 1
col 2
col 3
col 4
col 5
col 6
Which change at 2-ply?

36. Example 1-ply and 2-ply lookahead scores
It is O’s move. What scores does a 1-ply lookahead for O assign to each move?
|O| | | | | | |
|X| | | |O| |X|
|O| | | |X|O|X|
|X| | | |O|O|X|
|X| |X| |X|O|O|
|X| |O|O|O|X|X|
col 0
col 1
col 2
col 3
col 4
col 5
col 6 -1
100 50
100 50
100 50
Which change at 2-ply?

37. Example 1-ply and 2-ply lookahead scores
It is O’s move. What scores does a 1-ply lookahead for O assign to each move?
|O| | | | | | |
|X| | | |O| |X|
|O| | | |X|O|X|
|X| | | |O|O|X|
|X| |X| |X|O|O|
|X| |O|O|O|X|X|
col 0
col 1
col 2
col 3
col 4
col 5
col 6 -1
100 50 50 50
100 50
1-ply
col 0
col 1
col 2
col 3
col 4
col 5
col 6 -1
100
100
100 50
2-ply

38. Example 1-ply and 2-ply lookahead scores
|X| |X|O| | |O|
|X|O|O|X| |X|X|
|X|O|O|O| |O|X|
It is X’s move. What scores does a 2-ply lookahead for X assign to each move?
col 0
col 1
col 2
col 3
col 4
col 5
col 6

39. Example 1-ply and 2-ply lookahead scores
|X| |X|O| | |O|
|X|O|O|X| |X|X|
|X|O|O|O| |O|X|
It is X’s move. What scores does a 2-ply lookahead for X assign to each move?
col 0
col 1
col 2
col 3
col 4
col 5
col 6
100 50 -1

40. Practice b ‘X’ ‘O’ 0-ply scores for O: 1-ply scores for O:
col 0
col 1
col 2
col 3
col 4
col 5
col 6
0-ply scores for O:
col 0
col 1
col 2
col 3
col 4
col 5
col 6
1-ply scores for O:
col 0
col 1
col 2
col 3
col 4
col 5
col 6
2-ply scores for O:
col 0
col 1
col 2
col 3
col 4
col 5
col 6
3-ply scores for O:

41. Solutions b
‘X’
‘O’
col 0
col 1
col 2
col 3
col 4
col 5
col 6
0-ply scores for O: -1 50 50 50 50 50 50
col 0
col 1
col 2
col 3
col 4
col 5
col 6
1-ply scores for O: -1 50 50
100 50 50 50
col 0
col 1
col 2
col 3
col 4
col 5
col 6
2-ply scores for O: -1
100 50
col 0
col 1
col 2
col 3
col 4
col 5
col 6
3-ply scores for O: -1
100
100