Software Design Lecture Notes
Fall 2004

For Thursday you should:

1) read my Homework 7 solutions and make sure you understand
   this data structure design stuff.

2) work on your project

The exam is Friday, either 8-10 or 11-1.

Exam questions?


Homework 7 Solutions
--------------------

Some comments on my solutions:

1) in several cases, I demonstrate a specific version of a function
   (like analyze_wants) and then a more general version 
   (like analyze_attr)

   generalization is great, but at some point it starts to make
   programs hard to read.

2) the getattr and setattr functions make it relatively clean to
   generalize a function to work with unspecified attributes.

3) maybe I'm just a function junky, but I think it would be good
   (for most of you) to write smaller, simpler functions.

4) writing function comments often leads you to improve interfaces.


The output from my program is in 5 (unlabeled) columns

The sequence is a string with 1s for boys and 2s for girls

seq  n     wants%     spousewnts   intends

2073 people with one children
1 1036     51.44788    27.60618    23.74517
2 1037     50.72324    28.25458    24.01157
 
2657 people with two children
11 687     18.19505    12.37263    8.29694
12 733     17.59891    12.41473    8.73124
21 669     16.89088    10.16442    6.42750
22 568     19.71831    14.96479    10.21127
 
1415 people with three children
111 250     12.00000    7.20000    3.60000
112 205     12.68293    9.26829    4.87805
121 178     10.67416    6.74157    4.49438
122 179     12.84916    8.93855    4.46927
211 166     9.63855    6.02410    3.01205
212 156     8.97436    3.84615    1.92308
221 147     9.52381    8.16327    2.72109
222 134     9.70149    8.95522    4.47761
 
517 people with four children
1111 42     7.14286     4.76190    4.76190
2222 25     12.00000    12.00000    4.00000


By the way, if there is a bias toward having more children
if there is no boy, what effect does that have on the population?


Inheriting from built-in types
------------------------------

You can write classes that inherit from built-in types.  In fact,
we saw an example on the first day:

class Hist(dict):
    def __init__(self, s):
        for c in s:
            self[c] = self.get(c, 0) + 1
 
def is_anagram(s1, s2):
    return Hist(s1) == Hist(s2)

1) all the dictionary methods work on Hists

2) the dictionary operators, too


# a Filist is a list of strings that contains the contents of
# a file.  All the usual list operations can be applied to a
# Filist.

class Filist(list):
    def __init__(self, file=None, t=None):
        # if a file is provided, read the contents
        if file:
            self.file = file
            lines = [line for line in open(file)]
            self.extend(lines)
        # add any lines that are provided
        if t:
            self.extend(t)

    def __str__(self):
        return string.join(self, '')

    def join(self):
        # collapse the list of strings into a single long string
        self[:] = [str(self)]

    def prefile(self, file):
        # prepend the contents of the given file
        ft = Filist(file)
        self.insert(0, ft)

    def suffile(self, file):
        # append the contents of the given file
        ft = Filist(file)
        self.extend(ft)

    def writeto(self, file):
        # write the contents of the Filist to a file
        fp = open(file, 'w')
        for line in self:
            fp.write(line)

    def writeback(self):
        # write the contents of the Filist back to the file it came from
        self.writeto(self.file)

Notice that in addition to being a list, the Filist has an
additional attribute named file.


Try this:

wget http://wb/sd/code/Filist.py
python

from Filist import *
ft = Filist('Filist.py')
print ft[0]
print ft.file
print ft.__dict__
print ft


Threading
---------

Create a file named thread_example.py and type this in:

import string
from time import sleep
from threading import *

def loop(seq, delay=1):
    for x in seq:
        print x
        sleep(delay)

loop(range(3))

thread = Thread(target=loop, args=[string.lowercase, 0.4])
thread.start()

loop(string.uppercase)


1) thread diagrams

2) keyboard interrupt woes