CS 1MD3 - Winter 2006 - Assignment #2

Generated for Student ID: 0465698

Due Date: Wednesday, February 8th

(You are responsible for verifying that your student number is correct!)

Part 1: Debugging

The following four functions are infested with bugs. Correct them by adding or changing a single line in each one. Clearly indicate your changes with comments. If you add a line, append the comment, "# added." If you change a line, append a comment to it containing the original, erroneous line. Solutions submitted without comments will not be marked.

1

def hammingDistance(str1, str2):
	"""Returns the Hamming distance (or "edit distance") between two strings of the
	same length.  Hamming distance is defined as the minimum number of characters which
	must be changed	to make the strings identical.  For example, the Hamming distance
	between	"Python" and "Athlon" is 4 (only the last two letters are the same);
	the Hamming distance between "noodle" and "needle" is 2 (only the second and 
	third letters differ)."""
	if len(str1) != len(str2):
		return None
	list1 = list(str1)
	list2 = list(str2)
	n=len(list1)
	distance = 0
	i = n-1
	while i >= 0:
		if list1[i] != list2[i]:
			distance = distance + 1
		i=i+1	
	return distance

def product(numberList):
	"""Computes the product of all the list elements."""
	n = len(numberList)
	if n <= 0:
		return None
		theProduct = 1	
	i=0
	while i < n:
		theProduct = theProduct * numberList[i]
		i=i+1
	return theProduct

def mean(numberList):
	"""Returns the mean (i.e. average) value of the elements in the list"""
	n = len(numberList)
	if n == 0:
		return None
	theSum = 0
	i = n-1
	while i > 0: 
		x = numberList[i]
		theSum = theSum + x
		i = i - 1
	return float(theSum) / float(n)

def norm(aVector):
	"""Computes the Euclidian norm of the given vector in R^n.
	The Euclidean norm of x=(x1, x2, ..., xn) is defined as the square root of
	x1^2 + x2^2 + ... + xn^2."""
	n = len(aVector)
	if n <= 0:
		return None
	theNorm = 0
	i = 0
	whi1e i < n:	
		theNorm = theNorm + abs(aVector[i])**2
		i=i+1
	return pow(theNorm, 0.5)

Part 2: Testing

Create automated tests for the following function using PyUnit. Your tests should ensure that the code produces the expected result in all cases.

def median(aList):
	"""Returns the median of the given list, which is defined as the element which is no greater
	than half the elements, and no less than half the elements.  If the list contains an even
	number of elements, the median is traditionally the mean of the two such bisectors."""
	n = len(aList)
	if n == 0:
		return None
	if n == 1:
		return aList[0]
	# Make a deep copy of the list so as not to destroy it
	listCopy = []
	for x in aList:
		listCopy.append(x)
	# Do a (slow but simple) selection sort to put the elements in order
	for i in range(0,n-1):
		nextElmt = min(listCopy[i:n])
		j = i
		while listCopy[j] != nextElmt:
			j = j+1
		tmp = listCopy[i]
		listCopy[i] = listCopy[j]
		listCopy[j] = tmp
	# If there are an even number of elements, the median is the mean of the middle two
	print listCopy
	if 2*(n/2) == n:
		return (listCopy[n/2 - 1] + listCopy[n/2]) / float(2)
	else:
		return listCopy[n/2]