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I have a large nested loop called classarray full of information about different classes. I'm trying to combine the classes that are the same class, given that the data in the first 2 nest loop indexes are the same. 

[['AAS', '100', 'Intro Asian American Studies', '0', '12', '8', '5', '1', '3', '0', '0', '0', '0', '0', '0', '0', 'S-15']
['AAS', '100', 'Intro Asian American Studies', '1', '10', '4', '3', '6', '0', '1', '2', '0', '0', '0', '0', '0', 'S-15']
['AAS', '100', 'Intro Asian American Studies', '1', '7', '6', '7', '4', '1', '0', '1', '0', '0', '0', '0', '0', 'S-15']
['AAS', '120', 'Intro to Asian Am Pop Culture', '6', '7', '5', '2', '0', '3', '3', '0', '1', '0', '0', '0', '1', 'S-15']
['AAS', '215', 'US Citizenship Comparatively', '1', '3', '5', '4', '1', '6', '1', '3', '2', '1', '1', '1', '0', 'F-15']
['AAS', '258', 'Muslims in America', '0', '19', '2', '1', '0', '0', '0', '0', '0', '0', '0', '0', '0', 'S-16']
['AAS', '365', 'Asian American Media and Film', '1', '4', '6', '4', '5', '1', '3', '2', '2', '0', '0', '1', '0', 'S-16']
['AAS', '365', 'Asian American Media and Film', '6', '15', '0', '0', '1', '0', '3', '1', '1', '0', '0', '0', '2', 'S-15']]

I've written this code below to try to combine the rows and produce a new array called new_array:

itemx = ['','','',0,0,0,0,0,0,0,0,0,0,0,0,0,'']
newarray=[]
for course,courseplus1 in zip(classarray,classarray[1:]):
    if (course[0]==courseplus1[0] and course[1]==courseplus1[1]):
        itemx[0]=course[0]
        itemx[1]=course[1]
        itemx[2]=course[2]
        for number in range(3,16):
            itemx[number]=itemx[number]+(int(course[number])+int(courseplus1[number]))
        itemx[16]=course[16]
    else:
        newarray.append(itemx)
        print(itemx)
        itemx[0]=courseplus1[0]
        itemx[1]=courseplus1[1]
        itemx[2]=courseplus1[2]
        for number in range(3,16):
            itemx[number]=int(courseplus1[number])

for item in newarray:
    print(item)

However, the output is this:

['AAS', '365', 'Asian American Media and Film', '7', '19', '6', '4', '6', '1', '6', '3', '3', '0', '0', '1', '2', 'S-16']

5 times. From what I understood by looking through stack overflow, the reason is because:

newarray.append(itemx)

appends itemx to the list; itemx is one singular memory location that, at the end, has AAS 365's information in it. So, new array, as a list of itemx's, has a bunch of itemx's in it.

My question is: how do I deal with or mitigate this problem? To create classarray, I was doing the same thing, except i was declaring the itemx inside of the for loop, which i understand to mean itemx is a new variable with a new location.

wwii
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N. Patel
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  • Possible duplicate of [How to clone or copy a list?](http://stackoverflow.com/questions/2612802/how-to-clone-or-copy-a-list) – juanpa.arrivillaga Jan 10 '17 at 22:46
  • When you assign to `itemx` inside the loop, it is the *same variable* which gets a new reference assigned each iteration of the loop. Terminology note: there is no variable declaration in Python. – juanpa.arrivillaga Jan 10 '17 at 22:50

2 Answers2

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>>> from copy import copy, deepcopy
help(copy)
help(deepcopy)

>>> a = [1]
>>> b = copy(a)
>>> b.append(1)
>>> b
[1, 1]
>>> a
[1]
abcdn
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After consulting with some experienced friends, I was able to solve my problem. All I need to do is "redeclare" itemX in my else statement after appending itemx to newarray. This points it to a new location in memory (I think)! 

    else:
    newarray.append(itemx)
    itemx = ['', '', '', 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, '']
    itemx[0]=courseplus1[0]
    itemx[1]=courseplus1[1]
    itemx[2]=courseplus1[2]
    for number in range(3,16):
        itemx[number]=int(courseplus1[number])
N. Patel
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