Writing to a file in Python 3.x

Question

from arrayheap import ArrayHeap
    def generateTable(self, node, table):
        def codeTable(node, codeString):
            if node.isLeaf:
                table[node._char] = codeString
                return
            if node.getleft() is not None:
                table(node.getLeft(), codeString + '0')
            if node.getRight() is not None:
                table(node.getRight(), codeString + '1')
        codeTable(node, '')
        return(table)

def main():
    with open('codetable.txt', 'w') as cdt:
        codeTable = {}
        codeTable = HTree.generateTable(HTree, codeTable)
        for i in sorted(codeTable):
            cdt.write(str(i) + '\t' + str(codeTable[i]) + '\n')
main()

I am trying to output to a file the binary traversal to each individual node in a tree. I have left the preorder and postorder traversal methods in the file for reference. My question is what is wrong with my generateTable() method (most of the code was provided to me) I would like to output it so that it lists the traversal, 0 being left 1 being right, in the format <ascii value> : <binary path>. The thing is, when I run this code, my output file codetable.txt is empty. What am I doing wrong?

You open three different output files. Are you saying they are all empty? If not, which ones are you talking about? — BrenBarn, Apr 20 '14 at 21:15
I apologize. Only the generateTable() method isn't working. The preorder and inorder files and methods work fine. — somebody, Apr 20 '14 at 21:19
@somebody that function defines a nested function, then ignores it and immediately returns one of its arguments, unchanged. What did you expect it to do? — jonrsharpe, Apr 20 '14 at 21:21
It's not at all clear what you intend `generateTable` to do. As jonrsharpe says, it doesn't really do anything, and even if you called the nested function it defines, that nested function doesn't do anything either. — BrenBarn, Apr 20 '14 at 21:29

Martijn Pieters · Accepted Answer · 2014-04-20T21:49:19.057

generateTable() returns table unchanged; you passed in an empty dictionary, and the function does nothing else but return that same object.

The nested codeTable() function is not used; nothing ever actually calls it. Even if you unindented the codeTable(node, '') call to be outside of the nested function, that function has several flaws:

codeTable() only takes one argument, but the codeTable(node, '') call passes in two arguments.
It only ever references node.isLeaf but does not call it.
It treats table as both a dictionary and a callable.

I suspect you were meant to call it recursively; something like the following perhaps?

def generateTable(self, node, table):
    def codeTable(node, codeString):
        if node.isLeaf():
            table[node._char] = codeString
            return
        if node.getleft() is not None:
            codeTable(node.getLeft(), codeString + '0')
        if node.getRight() is not None:
            codeTable(node.getRight(), codeString + '1')
    codeTable(node, '')
    return(table)

This now generates a mapping with paths to leaf nodes, keyed by the value of the leafnode; the path consists of 0 and 1 characters denoting left and right nodes on the tree.

Once the table has been generated, the writing to a file can be simplified to:

for i in sorted(codeTable):
    cdt.write(str(i) + '\t' + str(codeTable[i]) + '\n')

I've done what you suggested, and I have called it that way, but it only prints the root node and nothing else. In this case the output file simply says "1082" I have revised my code above to reflect my current program. — somebody, Apr 20 '14 at 22:14
You are still not *calling* `node.isLeaf()`. A function object itself, uncalled, is always considered true so the function never recurses and instead just terminates right at the root node. — Martijn Pieters, Apr 20 '14 at 22:56
Add the missing `()`; look closely at the difference between my and your version. — Martijn Pieters, Apr 20 '14 at 23:00

Writing to a file in Python 3.x

1 Answers1