Question

I have created an object type.. and after initilializing I am pushing that into a list.
but for some reason the behavior is not as expected.
let me put in the sample code.. and then the output.

def allignDatesToWhenWasItemSold(pilotInstance):
    unitsSoldPerDay = pilotInstance._units_sold_per_day
    productPart = pilotInstance._product
    date = productPart._date
    quantity = pilotInstance._product._quantity

    listOfPilotInstance = []
    for i in range(len(unitsSoldPerDay)):
        perDayQuantity = unitsSoldPerDay[i]
        #modDate = date
        #print perDayQuantity
        modDate = modifyDate(date, i)
        productPart._date = modDate

        #print "pro ", productPart._date
        newPilotInstance = PilotTest(productPart, pilotInstance._name,perDayQuantity)
        print "here ",newPilotInstance._product._date._date, ' ',newPilotInstance._product._date._month, ' ', newPilotInstance._units_sold_per_day
        #newPilotInstance.setDate(modDate)

        listOfPilotInstance.append(newPilotInstance) #note this line.. this is where the trouble is
        for k in listOfPilotInstance:
            print k._product._date._date

    for ele in listOfPilotInstance:
        print "there " ,ele._product._date._date, ' ',ele._product._date._month, ' ',ele._units_sold_per_day
    return listOfPilotInstance

The out put are as following

here  30   7   1
30
here  31   7   0
31<--- now this shouldnt be like this.. as I am doing append.. teh first ele shoulnt be overwrited??
31
here  1   8   2
1
1
1
there  1   8   1
there  1   8   0
there  1   8   2

So my query is that since I am doing the append.. why is the date element getting overwrited?
Any clue as in what I am doing wrong?
Thanks

Answer 1

You are using the same productpart instance, and just mutating it:

productPart._date = modDate

Since all the PilotTest objects have a reference to the same productPart instance, all of them see the mutation.

You need to create a new instance of your class on each iteration through the loop and assign this new instance to productPart.

productPart = ...something here...