Merge pull request #3 from PythonCHB/master

week 4 pull request

Author: Divesh

PossibleTopics.md

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+This repository contains the demonstration software for the UW PCE Python 
+class.  The worked homework problems are in subdirectories.
+

README.txt

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+"""
+Precondition, postcondition, invariant
+
+A while-loop can be derived by filling in this template
+with blocks S and T and condition P
+that establish invariant I and postcondition I and not P
+
+    S
+    # pre: I
+    while (P):
+        # I
+        T
+    # post: I and not P
+"""
+
+def quotient(n, d):
+    """
+    Divide n by d, integer division by repeated subtraction
+    n: dividend, d: divisor, q: quotient, r: remainder
+    The definition of integer division is: n == q*d + r and r < d
+    """
+    assert n >= 0 and d > 0        # function precondition
+    r = n    
+    q = 0
+    # assert n == q*d + r            # loop precondition 
+    while (r >= d):
+        # assert n == q*d + r        # loop invariant
+        r = r - d
+        q = q + 1
+    # assert n == q*d + r and r < d  # postcondition
+    return q
+
+print '9/3 %s' % quotient(9,3)
+print '8/3 %s' % quotient(8,3)
+print '3/3 %s' % quotient(3,3)
+print '2/3 %s' % quotient(2,3)
+
+# what happens if preconditions are violated?

assertions.py

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+I dropped the penny
+The penny dropped I

ch_1/sentences.txt

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+#! /usr/bin/python
+#
+#
+s = "Level 0\n\tLevel 1\n\t\tLevel 2"
+print s
+
+# raw string, note the leading r
+r = r"Level 0\n\tLevel 1\n\t\tLevel 2"
+print r
+
+# Regular expressions with delimited strings
+re_1 = "\\w\\d{2,3}"
+print re_1
+
+re_2 = r"\w\d{2,3}"
+print re_2

raw_strings.py

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+#! /usr/bin/env python
+#
+# This prorgram reads in a list of students from a file, and sorts them in
+# random order
+#
+import sys
+import random
+import string
+import csv
+
+date_students = {0:"Oct 16th", 3:"Oct 23rd", 6:"Oct 30th", 9:"Nov 6th", \
+                 12:"Nov 13th", 16:"Nov 20th", 20:"Nov 27th", 24:"Dec 4th",
+                  28:"Dec 11th" }
+filename = "Student_list.csv"
+f = open(filename,"r")
+raw_student_list = csv.reader(f, delimiter='\t', quotechar='"')
+student_list = []
+for a_line in raw_student_list:
+# Column 0 is the student last name, Column 1 is the student first name 
+# student's name (last name first)
+    student_list.append( string.strip( a_line[0]+" "+a_line[1] ) )
+random.shuffle( student_list, )
+counter = 0
+for n in student_list :
+    if counter  in date_students.keys() :
+        print "----", date_students[counter]
+    counter += 1
+    print counter, n
+print "----"
+
+
+