Inheriting from the list object

[kdt]

Hi

I have a function for calculating the standard deviation of a list. I was wanting to create this as an object and inherit from pythons list object.

I'm pretty new to the whole OOP concept, can someone please have a look at my code to see why it prints an address rather than a value and where I'm messing this OOP thing up.

Thanks

class StandardDev(list):
    def __init__(self, theList):
        self.theList = theList
 
    def standardDev(self):
        import math
        sums = 0
        n = len(self)
        #Calculate the mean average
        ma = (1/float(n))*sum(self)
        for i, j in enumerate(self):
            sums += ((self[i]-ma)**2)
        return round(math.sqrt((1/float(n))*(sums)),2)
 
 
a = (5,6,8,9)
 
b = StandardDev(a)
print b.standardDev
 
 

[bvdet]

Hi

I have a function for calculating the standard deviation of a list. I was wanting to create this as an object and inherit from pythons list object.

I'm pretty new to the whole OOP concept, can someone please have a look at my code to see why it prints an address rather than a value and where I'm messing this OOP thing up.

Thanks

class StandardDev(list):
    def __init__(self, theList):
        self.theList = theList
 
    def standardDev(self):
        import math
        sums = 0
        n = len(self)
        #Calculate the mean average
        ma = (1/float(n))*sum(self)
        for i, j in enumerate(self):
            sums += ((self[i]-ma)**2)
        return round(math.sqrt((1/float(n))*(sums)),2)
 
 
a = (5,6,8,9)
 
b = StandardDev(a)
print b.standardDev
 
 

class StandardDev(list):
    def __init__(self, theList):
        self.theList = theList
 
    def standardDev(self):
        import math
        sums = 0
        n = len(self.theList)
        #Calculate the mean average
        ma = (1/float(n))*sum(self.theList)
        for i, j in enumerate(self.theList):
            sums += ((self.theList[i]-ma)**2)
        return round(math.sqrt((1/float(n))*(sums)),2)
 
 
a = (5,6,8,9)
 
b = StandardDev(a)
print b.standardDev()
 
'''
>>> 1.58
>>>
'''

[kdt]

cheers much again bvdet. your awesome!

[kdt]

sorry, last question. How best is it to catch integer division by zero errors on this code?

Thanks

[bvdet]

sorry, last question. How best is it to catch integer division by zero errors on this code?

Thanks

It looks like the only way that could happen is when the list is empty. A simple if statement will take care of that:

n = len(self.theList)
if n:
    ....... do stuff......

[kdt]

cheers mate :). I was thinking of using try except, but this works fine.

[bartonc]

It looks like the only way that could happen is when the list is empty. A simple if statement will take care of that:

n = len(self.theList)
if n:
    ....... do stuff......

Or simply:

if self.theList:
    ....... do stuff......