[XML-SIG] Element.firstChild() returns error

Martin v. Loewis martin@loewis.home.cs.tu-berlin.de
Tue, 7 Nov 2000 01:23:14 +0100

> By pawing around in the code, I discovered that instead of using
> getFirstChild() I should use firstChild() on a Node. So first
> question, is there a documented Python language binding to the DOM?

There will be RSN. Unfortunately, it was not completed in time for
2.0, and currently sits on a machine at BeOpen which is currently

The core of your problem here is that IDL attributes map to attributes
in Python, instead of accessor functions as in Java. For compatibility
with the Python CORBA mapping, 4DOM also supports the an accessor
function _get_<name>.

> >>> acctList1
> <Element Node at 9131308: Name = 'Accounts' with 0 attributes and 3
> children>
> >>> acctList1.firstChild()
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
> AttributeError: no __call__ method defined
> Is this an error in the implementation or in my use?

It's your use. accList1.firstChild *is* the first child, no need to
call it.

> Finally, I noticed the javadom.py module. The comments indicate that
> this module is to allow access to Java implementations from
> Python. What I was hoping for was a wrapper to provide the Java IF's
> to the Python implementation! Is this a reasonable request or am I
> up the wrong tree?

No, I believe that's something different: It gives you access to a
Java DOM implementation inside JPython, with exposes the official
Python DOM mapping of the Java DOM tree (instead of the one resulting
from the Java mapping).

However, it should not be too difficult to get used to this mapping;
apart from the attributes issue, there really is no deviation from the
straight-forward mapping (except that DOMStrings can sometimes appear
as Unicode strings and sometimes as byte strings - depending on the
Python version).

One more difference, perhaps: the Python mapping offers convenience
container objects instead of following the IDL-style containers: e.g.
a NodeList might be accessible as a Python sequence. "might be", since
it is a list in minidom (i.e. no .item, .length), and an object
following the IDL mapping in 4DOM (i.e. no __getitem__, __len__). I
hope this can be fixed so that you can always treat .childNodes as a
list.  If you only use .firstChild, .nextSibling, you won't even
notice that difference.