如何使用lxml检查每个元素中的xmlns

Question

I am using lxml to check Product elements as they stream in a MapReduce job. I am trying to make sure that only the correct xmlns value is present in every element. For example, every Product element should have an xmlns set to " http://mynetwork.products.com/new ":

<Product xmlns="http://mynetwork.products.com/new">

As I check each Product element (streamed one at a time), I just want to make sure that it looks like the above. I want to check for the following potential errors:

1. Incorrect xmlns URL:

<Product xmlns="http://mynetwork.products.com/old">

2. Missing URL

<Product xmlns="">

3. Missing xmlns key/value pair

<Product>

4. Extra attribution in the Product element

<Product xmlns="http://mynetwork.products.com/new" something="else">

I tried storing the value of Product.nsmap for each element (which is a dictionary) and then reading the values of the dictionary to validate, but it doesn't help me detect any of the below cases. There must be a way.

Answer 1

You can check combination of nsmap and attrib properties of each Product element. nsmap should contains only one key value pair ie key None with value "http://mynetwork.products.com/new" , and attrib should be empty since you won't allow any attributes in the element.

Brief example (pyhon 2.7) :

>>> from lxml import etree
>>> raw = '''<root>
... <Product xmlns="http://mynetwork.products.com/new"/>
... <Product xmlns="http://mynetwork.products.com/new" something="else"/>
... <Product xmlns="http://mynetwork.products.com/old" />
... <Product xmlns=""/>
... <Product/>
... </root>'''
... 
>>> root = etree.fromstring(raw)
>>> for p in root.findall('*'):
...     isValid = len(p.nsmap) == 1 \
...         and p.nsmap[None] == 'http://mynetwork.products.com/new' \
...         and not p.attrib
...     print isValid
... 
True
False
False
False
False