Python: Help Improving Recursive Function

Question

I have the following function and from time to time it returns the error "global name 'x' is not defined" which occurs when it jumps to the return statement. I would like help improving this code without losing functionality. Any insight would be greatly appreciated.

 def label(tree, instance, class_labels):
     '''Returns the label at the end of every "branch" in the tree'''
     global x
     for row in tree:
        if row[0] == instance[row[1]]:
            if row[2][0] in class_labels:
                x = row[2][0]
                 return x
            else:
                x = label(row[2], instance, class_labels)
    return x

Is there any reason for using global x in this code? You're not accessing it in the code, and you're already returning it, so what is the purpose of making x global? (And the reason why it complains is because if it jumps straight to x the variable x would be undefined.) — Rufflewind
– Rufflewind, Commented Dec 3, 2014 at 6:08
Rufflewind's comment is the answer (plus a bit of good advise) — Francisco Meza
– Francisco Meza, Commented Dec 3, 2014 at 6:13

doog abides · Accepted Answer · 2014-12-03 06:20:05Z

2

This may help...

def label(tree, instance, class_labels):
    '''Returns the label at the end of every "branch" in the tree'''
    last = None
    for row in tree:
        if row[0] == instance[row[1]]:
            if row[2][0] in class_labels:
                return row[2][0]
            next = label(row[2], instance, class_labels)
            if next is not None:
                 last = next
    return last

answered Dec 3, 2014 at 6:20

doog abides

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2 Comments

user3318660 Over a year ago

this works to an extent but I am having issues because when it jumps to the return statement it's obviously none and that is causing a problem

doog abides Over a year ago

You probably have a problem with your data in your tree. It's quite impossible to tell without knowing the structure and actual data. Trees don't really have "rows" for one thing..

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