Question

when I run this program, it print NameError global name 'viewAll' is not defined

I’ m a C programmer, I didn’t know why.

viewAll(this) is defined in class binTree,

Platform:Python 2.7 in windows 7 64 bit

#!/usr/bin/python
#-*-coding:gbk-*-

class binTree():
    def __init__(this, left = None, right = None, data = 0):
        if data == 0:
            this = None
        else:
            this.leftNode = left
            this.rightNode = right
            this.data = data
    def viewAll(this):
        if this != None:
            print this.data,
            viewAll(this.leftNode)
            viewAll(this.rightNode)

def creatBT():
    temp = input('Please input a number, input "0" for end!')
    if temp == 0:
        return None
    else:
        tree = binTree()
        tree.data = temp
        tree.leftNode = creatBT()
        tree.rightNode = creatBT()
        return tree

if __name__ == "__main__":
    root = creatBT()
    root.viewAll()

Answer 1

You need to do a Python tutorial — you’re not understanding how the instance object works in Python instance methods.

Your problem is here:

def viewAll(this):
    if this != None:
        print this.data,
        viewAll(this.leftNode)
        viewAll(this.rightNode)

You need to access viewAll on the instance you want to call it on:

def viewAll(this):
    if this != None:
        print this.data,
        this.leftNode.viewAll()
        this.rightNode.viewAll()

I’m not sure what you’re intending to do here:

    if data == 0:
        this = None

but all you are actually doing is pointing the name this at None in the scope of that one function call. It doesn’t change anything about the class instance or anything outside the function.

So, in viewAll,

    if this != None:

will always be True, because this is again the instance you’ve called viewAll on — it hasn’t been and can’t be set to None.

---

class binTree():
    # I removed __init__ to show you weren't using it
    def viewAll(self):
        print self.data,
        # don't try to show a node that is empty
        if self.leftNode:
            self.leftNode.viewAll()
        if self.rightNode:
            self.rightNode.viewAll()

def creatBT():
    try:
        # don't use input
        temp = int(raw_input('Please input a number, input "0" for end!'))
    except ValueError:
        # in case they don't put in a number
        temp = 0
    if temp == 0:
        return None
    else:
        tree = binTree()
        tree.data = temp
        tree.leftNode = creatBT()
        tree.rightNode = creatBT()
        return tree

if __name__ == "__main__":
    root = creatBT()
    # don't try to show the nodes if none were created
    if root:
        root.viewAll()