Transcript Object-Oriented Programming in Python Goldwasser and

Object-Oriented Programming in Python
Goldwasser and Letscher
Chapter 7
Good Software Practices
Terry Scott
University of Northern Colorado
2007 Prentice Hall
Introduction: Chapter 7 Topics
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Mastermind game.
Top down design and bottom up implementation.
Mastermind Design.
Naming Conventions.
Python Docstreams.
Encapsulation.
Modules and Unit Testing.
Error Checking.
Mastermind with graphical user input (GUI).
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Overview of Mastermind
• One player makes up a pattern of colored pegs.
• The other player tries to guess the pattern.
• For each guess there are two numbers given:
– black is the number of pegs in the guessed
pattern that match at the same spots with those in
the original pattern.
– white is the number of colored pegs in the
guessed string that are in the original but not in
the right positions.
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Mastermind Game During Play on
the Left and at End on the Right.
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Building a Larger Program
• Top-down design:
– Design looks at the overall program.
– Followed by more and more detail.
• Bottom-up Implementation:
– Build program starting at bottom details.
– Followed by putting details together.
– Until final program is completed.
• Smaller pieces for making program is called
modularity. Modularity promotes code reuse.
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Top-down Design and Bottom-up
Implementation
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Example: Text-Based Mastermind
Session
How many pegs are in the secret color code (1 to 10)?
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How many colors are available (2 to 8)? 5
How many turns are allowed (1 to 20)? 10
Enter a guess (colors are RBGWY): RRRRR
On turn 1 of 10 guess RRRRR scored 1 black and 0
white.
Enter a guess (colors are RBGWY): RBBBB
On turn 2 of 10 guesses RBBBB scored 0 black and 1
white.
...
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Mastermind Major Components
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Sequence Diagram for Mastermind
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Methods for Mastermind
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Naming Conventions
• classes – capitalize first letter.
• functions – first letter small, if suceeding
words then they should be capitalized.
• data – same as functions.
• parameters – same as functions.
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Formal Documentation
• Any string following a # is ignored by the
Python interpreter.
– used by programmer looking at code.
• Triple double quotes around comments
makes docstrings.
– visible in the code.
– use pydoc to pull out comments.
– help() will pull out these comments.
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Webpage Created by pydoc
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Television Class with docstrings
def __init__(self):
"""Create a new Television instance.
The power is initially off. The first time
the TV is turned on, it will be set to
channel 2 with a volume level of 5
(unmuted)"""
#use previous code
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Encapsulation
• The internal details of the software are
hidden from the user.
• Python uses the class concept to hide the
details of the software.
• The behavior of the object is separate
from how it is implemented.
• This is called abstraction and helps the
software designer not to be bogged down
in the details of the object.
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Underscored Names
• Python does not enforce keeping data as
private (not accessible from outside the
class).
• The underscore in front of identifiers
prevents pydoc or other documentation
from having that item displayed.
• Sometimes methods are only used within
the class. These are called private
methods.
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Unit Testing
• Larger software projects may consist of
many files/classes.
• Waiting too long before testing may result
in many errors which are difficult to find
and fix.
• The solution is to test each module as it is
developed.
• The unit test in Python can help with
testing each module.
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Unit Testing (continued)
class Pattern:
#implementation
if __name__ == '__main__':
#unit test here
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Pattern Class with Unit Test
from Score import Score
from random import seed, randint
class Pattern:
def __init__(self, numPegs):
"""construct a new pattern"""
self._pegList = [0] * numPegs
def __len__(self):
"""return length of current pattern
return len(self._pegList)
def getPegColor(self, index):
"""Returns current color setting of the peg at
index"""
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Pattern Class with Unit Test
(continued)
def setPegColor(self, index, colorID):
"""set color of peg at index location"""
self._pegList[index] = colorID
def compareTo(self, otherPattern):
"""compare and score otherPattern to current
pattern"""
black = 0
for i in range(len(self._pegList)):
if
self.getPegColor(i)==otherPattern.getPegColor(i):
black += 1
colorsUsed = [ ]
for color in self._pegList:
if color not in colorsUsed:
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Pattern Class with Unit Test
(continued)
white = 0
for color in colorsUsed:
white += min(self._pegList.count(color),
otherPattern._pegList.count(color))
white -= black
return Score(black, white)
def randomize(self, numColors):
"""Make a random pattern"""
seed()
for i in range(len(self._pegList)):
self._pegList[i] = randint(0, numColors – 1)
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Pattern Class with Unit Test
(continued)
#unit test for the Pattern class
if __name__ == '__main__':
modelA = (1, 3, 0, 3, 2)
patternA = Pattern(5)
for i in range(len(modelA):
patternA.setPegColor(I, modelA[i])
if len(patternA) != 5:
print 'Pattern length is miscalculated'
for i in range(5):
if patternA.getPegColor(i) != modelA[i]:
print 'Color at index', i, 'not properly set/
retrieved'
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Pattern Class with Unit Test
(continued)
copy = Pattern(5)
for I in range(5):
copy.setPegColor(i,patternA.getPegColor(i))
score = patternA.compareTo(copy)
if score.getNumBlack()!=5 or
score.getNumWhite()!=0:
print 'Score miscalculated'
#can repeat this for another pattern.
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Error Testing
• It is important to check user inputs to
prevent input errors from crashing the
program.
• Possible errors in Mastermind
– 3 beginning integers.
– at end when asked to play again.
– color pattern during playing of game.
• Code on next page shows how to check
some of these errors.
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User Error Checking for
Mastermind
#This is included in the class
def _readInt(self, prompt, small, large):
prompt=prompt+'(from '+str(small)+' to '+str(large) + ')?'
answer = small – 1
while not small <= answer <= large:
try:
answer = int(raw_input(prompt)
if not small <= answer <= large:
print 'Integer must be from ' + str(small) + ' to '
+ str(large) + '.'
except ValueError:
print 'That is not a valid integer.'
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return answer
Further Code
• Book pages 259 – 260 has further error
checking code.
• If the text based code is organized such
that the input and output are separate
methods, then converting to a GUI will be
less trouble.
• See pages 264 – 266 in the book to see
the code for the game using a GUI
interface.
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