Python3 Recursion, Avoiding variable changes to reflect globally within different recursive calls

Question

When using recursion in python3 let's say I have a function 'f(a,b)'.('b' is list) And within 'f' I am calling 'f' several times recursively. If a daughter instance of 'f' makes some changes to list 'b' how do I avoid those changes in 'b' to be reflected in the calling parent f? (I am not returning 'b'). For e.g. have a look at my code below. In the second elif I am making two recursive calls to the function goToDepth. If one of the called instance makes a change to depthArr , the change is being reflected in the calling function's copy of depthArr as well which I don't want. How to avoid that? Thanks a lot in advance!

def goToDepth(headNode,depthArr):
    if(headNode==None):
        return
    elif(not depthArr):
        return
    elif(depthArr[-1]!=1):
        depthArr[-1]=depthArr[-1]-1
        goToDepth(headNode.left,depthArr)
        goToDepth(headNode.right,depthArr)
    elif (depthArr[-1]==1):    
        headNode.left,headNode.right=headNode.right,headNode.left
        depthArr.pop()
        goToDepth(headNode.left,depthArr)
        goToDepth(headNode.right,depthArr)
    else:
        return

Alfe · Accepted Answer · 2017-03-03 11:33:37Z

1

Try passing copies of your list: a[:] creates a shallow copy.

Use the copy module to create deep copies (but that's probably bad design).

answered Mar 3, 2017 at 11:33

Alfe

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