I decided not to customize the xml-parser to fit the structure of a xml-document, but to make a parser that adapts the structure of the document. By converting the xml-document in this way, the access to the elements is simple and code-customization is minimal.
| Python |
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xmlreader.py:
==================================================
from xml.dom.minidom import parse
class NotTextNodeError:
pass
def getTextFromNode(node):
"""
scans through all children of node and gathers the
text. if node has non-text child-nodes, then
NotTextNodeError is raised.
"""
t = ""
for n in node.childNodes:
if n.nodeType == n.TEXT_NODE:
t += n.nodeValue
else:
raise NotTextNodeError
return t
def nodeToDic(node):
"""
nodeToDic() scans through the children of node and makes a
dictionary from the content.
three cases are differentiated:
- if the node contains no other nodes, it is a text-node
and {nodeName:text} is merged into the dictionary.
- if the node has the attribute "method" set to "true",
then it's children will be appended to a list and this
list is merged to the dictionary in the form: {nodeName:list}.
- else, nodeToDic() will call itself recursively on
the nodes children (merging {nodeName:nodeToDic()} to
the dictionary).
"""
dic = {}
for n in node.childNodes:
if n.nodeType != n.ELEMENT_NODE:
continue
if n.getAttribute("multiple") == "true":
# node with multiple children:
# put them in a list
l = []
for c in n.childNodes:
if c.nodeType != n.ELEMENT_NODE:
continue
l.append(nodeToDic(c))
dic.update({n.nodeName:l})
continue
try:
text = getTextFromNode(n)
except NotTextNodeError:
# 'normal' node
dic.update({n.nodeName:nodeToDic(n)})
continue
# text node
dic.update({n.nodeName:text})
continue
return dic
def readConfig(filename):
dom = parse(filename)
return nodeToDic(dom)
def test():
dic = readConfig("sample.xml")
print dic["Config"]["Name"]
print
for item in dic["Config"]["Items"]:
print "Item's Name:", item["Name"]
print "Item's Value:", item["Value"]
test()
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sample.xml:
==================================================
<?xml version="1.0" encoding="UTF-8"?>
<Config>
<Name>My Config File</Name>
<Items multiple="true">
<Item>
<Name>First Item</Name>
<Value>Value 1</Value>
</Item>
<Item>
<Name>Second Item</Name>
<Value>Value 2</Value>
</Item>
</Items>
</Config>
==================================================
output:
==================================================
My Config File
Item's Name: First Item
Item's Value: Value 1
Item's Name: Second Item
Item's Value: Value 2
|
Discussion
The big advantage of this recipe is that you never define the structure of the xml-document, you just use it.
One thing that bothers me, is that you must define 'multiple="true"' in the attribute of an element, if you want its children to be put in a list.
Comments
An alternate solution. Good idea. See my xml2obj recipe which is a variation on the theme that uses the expat parser for lower overhead and a stack to keep track of parents.
Check out pyRXP. pyRXP from Reportlab turns XML into a python tuple tree and is extremely fast. Check it out (http://www.reportlab.com/xml/pyrxp.html)
buglet? Shouldn't the first
be outdented one level? Otherwise, it's adding the partially-built list to the dictionary every time through the loop. (Or maybe it's late and I'm seeing double. ;-)
Improvement? Great idea! Very nice for small config. It is also good to add something like this:
Another improvent? How about this as an alternative to allow it to work without specifying the multiple attribute?
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