Thanks for the reply. I understand, but if self.value is any number other then 0, then the "for" will append to the square list, in which case square_list will always have some len greater than 0 when "value" is greater than 0?
I'm just trying to understand the mechanics. I'm assuming that isn't the way the statement is evaluated? When I get home from work I'll work around it. Is this an occasion which is best suited for a try:, except statement? Or should it, in general, but checked with "if's". Which is more expensive? The rest of the code was in the prior email (please see below) Module 1: import Statistics a = [1,2,3,4,5,6,7,8,9,10] mean = Statistics.stats.mean(*a) median = Statistics.stats.median(*a) var = Statistics.stats.variance(*a) print(mean, median, var) print() Module 2: #!/usr/bin/python # Filename: Statistics.py import math value_list = [] class Statistics: def __init__(self, *value_list): self.value = value_list #self.average = mean(*value_list) self.square_list= [] def mean(self, *value_list): if len(self.value) == 0: ave = 0 else: ave = sum(self.value) / len(self.value) return ave def median(self, *value_list): if len(self.value) <= 2: n = self.mean(self.value) elif len(self.value) % 2 == 1: m = (len(self.value) - 1)/2 n = self.value[m+1] else: m = len(self.value) / 2 m = int(m) n = (self.value[m] + self.value[m+1]) / 2 return n def variance(self, *value_list): if self.value == 0: var = 0 else: average = self.mean(*self.value) for n in range(len(self.value)): square = (self.value[n] - average)**2 self.square_list.append(square) var = sum(self.square_list) / len(self.square_list) return var stats = Statistics(*value_list) On Wed, Feb 24, 2010 at 5:59 PM, ALAN GAULD <alan.ga...@btinternet.com>wrote: > Forwarding to the list. > Please alweays use Reply All so others can comment too. > > I made a few changes, but I'm getting the same error on variance (see > below): > > Looks like a different error to me! > > It would seem to me that it should never evaluate if the denominator is > zero because of the if statement. > > But the if statement doesn't test whether len(self.square_list) is zero. > It tests whether self.value is zero. > > The other thing I don't understand is that the object that is being passed > into the instance is a list, but it seems to be a tuple once the object is > called. Why does this happen? Am I doing something additional wrong? > > Sorry, your code doesn't show any instances let alone lists being pased in? > > Alan G. > > File "C:\Python31\Lib\COI\Project\Statistics.py", line 39, in variance > var = sum(self.square_list) / len(self.square_list) > ZeroDivisionError: int division or modulo by zero > > #!/usr/bin/python > # Filename: Statistics.py > > import math > value_list = [] > class Statistics: > def __init__(self, *value_list): > self.value = value_list > #self.average = mean(*value_list) > self.square_list= [] > def mean(self, *value_list): > if len(self.value) == 0: > ave = 0 > else: > ave = sum(self.value) / len(self.value) > return ave > > def median(self, *value_list): > if len(self.value) <= 2: > n = self.mean(self.value) > elif len(self.value) % 2 == 1: > m = (len(self.value) - 1)/2 > n = self.value[m+1] > else: > m = len(self.value) / 2 > m = int(m) > n = (self.value[m] + self.value[m+1]) / 2 > return n > def variance(self, *value_list): > if self.value == 0: > var = 0 > else: > average = self.mean(*self.value) > for n in range(len(self.value)): > square = (self.value[n] - average)**2 > self.square_list.append(square) > var = sum(self.square_list) / len(self.square_list) > return var > > > On Wed, Feb 24, 2010 at 4:02 AM, Alan Gauld <alan.ga...@btinternet.com>wrote: > >> >> "James Reynolds" <eire1...@gmail.com> wrote >> >> >> This thread inspired me to start learning object oriented as well, but it >>> seems I must be missing something fundamental. >>> >> >> No, this has nothing to do with objects, its just a broken algorithm. >> >> median = Statistics.stats.median(*a) >>> n = (self.value[m] + self.value[m+1]) / 2 >>> IndexError: tuple index out of range >>> >>> def median(self, *value_list): >>> if len(self.value) % 2 == 1: >>> m = (len(self.value) - 1)/2 >>> n = self.value[m+1] >>> else: >>> m = len(self.value) / 2 >>> m = int(m) >>> n = (self.value[m] + self.value[m+1]) / 2 >>> return n >>> >> >> Consider the case where the length of value is 2. >> We will use the else part of the branch. >> m will have value 1 >> The highest index is 1 because indexes start at zero >> so value[m+1] will fail with an index error. >> >> A similar error will happen when the list has only 1 entry >> since the highest index there will be zero. >> >> You need to rethink your rules for generating the indexes >> remembering that they start at zero. >> >> >> >> -- >> Alan Gauld >> Author of the Learn to Program web site >> http://www.alan-g.me.uk/ >> >> _______________________________________________ >> Tutor maillist - Tutor@python.org >> To unsubscribe or change subscription options: >> http://mail.python.org/mailman/listinfo/tutor >> > >
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