Minidom.Node doesn't call __getattr__

[ArseAssassin]

I'm using minidom to parse XML and to simplify accessing child nodes, I'm trying to implement __getattr__ for the Node class. Yes, I know what most of you will think of that; I'll just have to be careful, won't I. ;)

import xml
from xml.dom.minidom import parseString
 
def getChild(self, name):
    print "Getting child"
    return self.getElementsByTagName(name)[0]
 
xml.dom.minidom.Node.__getattr__ = getChild
 
xmlDoc = parseString('''<?xml version="1.0" encoding="ISO-8859-1"?>
<CATALOG>
  <cd>
    <title>Empire Burlesque</title>
    <ARTIST>Bob Dylan</ARTIST>
    <COUNTRY>USA</COUNTRY>
    <COMPANY>Columbia</COMPANY>
    <PRICE>10.90</PRICE>
    <YEAR>1985</YEAR>
  </cd>
  <cd>
    <title>Hide your heart</title>
    <ARTIST>Bonnie Tylor</ARTIST>
    <COUNTRY>UK</COUNTRY>
    <COMPANY>CBS Records</COMPANY>
    <PRICE>9.90</PRICE>
    <YEAR>1988</YEAR>
  </cd>
</CATALOG>''')
 
xmlRoot = xmlDoc.childNodes[0]
print xmlRoot.__getattr__
print xmlRoot.cd.title.childNodes[0].nodeValue

outputs:

<bound method Element.getChild of <DOM Element: CATALOG at 0x1c50850>>
  File "C:\Users\Tuomas\Projektit\wrestlevania\ezXML.py", line 31, in <module>
    print xmlRoot.cd.title.childNodes[0].nodeValue
AttributeError: Element instance has no attribute 'cd'

As far as I can tell, everything works fine, except __getattr__ never gets called. Can anyone help me understand why that is or how to work around it?

[jlm699]

If you're trying to call __getattr__ you need ().

[ArseAssassin]

If you're trying to call __getattr__ you need ().

Not trying to call it - I'm overriding it.

[jlm699]

Not trying to call it - I'm overriding it.

No I know that... but you still need the (name) arguments that getChild needs

[ArseAssassin]

No I know that... but you still need the (name) arguments that getChild needs

I'm not sure what you're getting at. getChild is just an implementation of the special method __getattr__, which should be called when I'm trying to access attributes that aren't defined.

[jlm699]

I'm not sure what you're getting at. getChild is just an implementation of the special method __getattr__, which should be called when I'm trying to access attributes that aren't defined.

But aren't you over-riding __getattr__ with getChild ? The way that your code is setup, instead of __getattr__ being called, it calls for getChild... I don't know, maybe I'm misunderstandin g what you're trying to accomplish in this code... Where does the .cd. method come from since it's not an attribute of the class that you are trying to call it from?

[bvdet]

I'm using minidom to parse XML and to simplify accessing child nodes, I'm trying to implement __getattr__ for the Node class. Yes, I know what most of you will think of that; I'll just have to be careful, won't I. ;)

import xml
from xml.dom.minidom import parseString
 
def getChild(self, name):
    print "Getting child"
    return self.getElementsByTagName(name)[0]
 
xml.dom.minidom.Node.__getattr__ = getChild
 
xmlDoc = parseString('''<?xml version="1.0" encoding="ISO-8859-1"?>
<CATALOG>
  <cd>
    <title>Empire Burlesque</title>
    <ARTIST>Bob Dylan</ARTIST>
    <COUNTRY>USA</COUNTRY>
    <COMPANY>Columbia</COMPANY>
    <PRICE>10.90</PRICE>
    <YEAR>1985</YEAR>
  </cd>
  <cd>
    <title>Hide your heart</title>
    <ARTIST>Bonnie Tylor</ARTIST>
    <COUNTRY>UK</COUNTRY>
    <COMPANY>CBS Records</COMPANY>
    <PRICE>9.90</PRICE>
    <YEAR>1988</YEAR>
  </cd>
</CATALOG>''')
 
xmlRoot = xmlDoc.childNodes[0]
print xmlRoot.__getattr__
print xmlRoot.cd.title.childNodes[0].nodeValue

outputs:

<bound method Element.getChild of <DOM Element: CATALOG at 0x1c50850>>
  File "C:\Users\Tuomas\Projektit\wrestlevania\ezXML.py", line 31, in <module>
    print xmlRoot.cd.title.childNodes[0].nodeValue
AttributeError: Element instance has no attribute 'cd'

As far as I can tell, everything works fine, except __getattr__ never gets called. Can anyone help me understand why that is or how to work around it?

Modify getChild() slightly:

def getChild(self, name):
    print "Getting child"
    return self.getElementsByTagName(name)

Modify the calls:

xmlRoot = xmlDoc.childNodes[0]
print xmlRoot.__getattr__('cd')
print xmlRoot.__getattr__('cd')[0].__getattr__('title')[0].firstChild.nodeValue
print xmlRoot.__getattr__('ARTIST')[0].firstChild.nodeValue

Output:

>>> Getting child
[<DOM Element: cd at 0x100d4b8>, <DOM Element: cd at 0x100d788>]
Getting child
Getting child
Empire Burlesque
Getting child
Bob Dylan
>>> 

[jlm699]

Modify the calls:

print xmlRoot.__getattr__('cd')
 

That's what I was trying to say by using the (name) argument

[bvdet]

That's what I was trying to say by using the (name) argument

And you were correct!

[jlm699]

xmlRoot = xmlDoc.childNodes[0]
print xmlRoot.__getattr__('cd')
print xmlRoot.__getattr__('cd')[0].__getattr__('title')[0].firstChild.nodeValue
print xmlRoot.__getattr__('ARTIST')[0].firstChild.nodeValue

Output:

>>> Getting child
[<DOM Element: cd at 0x100d4b8>, <DOM Element: cd at 0x100d788>]
Getting child
Getting child
Empire Burlesque
Getting child
Bob Dylan
>>> 

In my calls I needed to modify it a little bit...

>>> xmlRoot.__getattr__('cd').__getattr__('title').firstChild.nodeValue
Getting child
Getting child
u'Empire Burlesque'
>>> xmlRoot.__getattr__('ARTIST').firstChild.nodeValue
Getting child
u'Bob Dylan'
>>>