[Tutor] Strange list behaviour in classes

[ALAN GAULD]

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.gauld at btinternet.com> wrote:
>
>
>>>>"James Reynolds" <eire1130 at 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 at python.org
>>>>To unsubscribe or change subscription options:
>>http://mail.python.org/mailman/listinfo/tutor
>>
>
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