checking whether an xml.dom node already exists

[gundarap]

Hello all,
I'm working on minidom.
My goal is to see whether an element already exists in the xml file before adding. I was using getElementsByTagName() to check weather the element already exists.
The code looks something like this:
Value = argv[1]

a = dom.getElementsByTagName(Name)[0].childNodes[0].nodeValue
     if (a!=Value):
        add elements.
    else:
        return

This part gives me index error index out of range.
Can you people suggest me a good solution.
Is there any other method which I can use to find the element already exists or not in an xml file.
Thanks in advance.

[bartonc]

To find out which list is giving the index error, break up that one-liner (always preferable):

a = dom.getElementsByTagName(Name)[0].childNodes[0].nodeValue

should be [example only - I'm not looking at the interface that you are using]:

elements = dom.getElementsByTagName(Name)
if elements:
    parentOfNodes = elements[0]
    nodeList = parentOfNodes.childNodes
    zerothNode = nodeList[0]
    thisNodeValue = zerothNode.nodeValue
else:
    print "empty list"

That way when an error occurs, you'll know which list has is empty.

Next step would be to wrap each one in if statements or try blocks.

[gundarap]

Sorry for the late reply.
That was really great.
I found one solution to check whether the node exists by using the getElementsBytagName method.I used this simple if statement to getrid of index error.
if(len(dom.getElementsByTagName(Name))!=0):
print "already exists"
This worked well.
Thanks for your valuable suggestions.
I will try to follow your suggestions to avoid this type of errors.

To find out which list is giving the index error, break up that one-liner (always preferable): should be [example only - I'm not looking at the interface that you are using]:

elements = dom.getElementsByTagName(Name)
if elements:
    parentOfNodes = elements[0]
    nodeList = parentOfNodes.childNodes
    zerothNode = nodeList[0]
    thisNodeValue = zerothNode.nodeValue
else:
    print "empty list"

That way when an error occurs, you'll know which list has is empty.

Next step would be to wrap each one in if statements or try blocks.

[bartonc]

Sorry for the late reply.
That was really great.
I found one solution to check whether the node exists by using the getElementsBytagName method.I used this simple if statement to getrid of index error.
if(len(dom.getElementsByTagName(Name))!=0):
print "already exists"
This worked well.
Thanks for your valuable suggestions.
I will try to follow your suggestions to avoid this type of errors.

I need to know which module you are using, so that I can give this thread a better title. Thanks.

[EDIT: never mind. I found it.]

[gundarap]

I used xml.dom.minidom..