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What is the position hash value and what does it do in XML?

When using XML in something like Python, (e.g. xml Python package) and calling getchildren() on a tag, the output is often of the form:
[<Element 'date' at 0x2b15236f4e08>]
...but what is the name of this bit 0x2b15236f4e08? Is it the position of the tag in the file? I can't find out anywhere what it means!

0x2b15236f4e08 is the identity of a Python object which, in this case, represents a particular XML element named date. It has no meaning at the XML level; it's an implementation detail at the Python level.

Parsing Google Earth KML file in Python (lxml, namespaces)

I am trying to parse a .kml file into Python using the xml module (after failing to make this work in BeautifulSoup, which I use for HTML).
As this is my first time doing this, I followed the official tutorial and all goes well until I try to construct an iterator to extract my data by root iteration:
from lxml import etree
tree=etree.parse('kmlfile')
Here is the example from the tutorial I am trying to emulate:
If you know you are only interested in a single tag, you can pass its name to getiterator() to have it filter for you:
for element in root.getiterator("child"):
print element.tag, '-', element.text
I would like to get all data under 'Placemark', so I tried
for i in tree.getiterterator("Placemark"):
print i, type(i)
which doesn't give me anything. What does work is:
for i in tree.getiterterator("{http://www.opengis.net/kml/2.2}Placemark"):
print i, type(i)
I don't understand how this comes about. The www.opengis.net is listed in the tag at the beginning of the document (kml xmlns="http://www.opengis.net/kml/2.2"...) , but I don't understand
how the part in {} relates to my specific example at all
why it is different from the tutorial
and what I am doing wrong
Any help is much appreciated!

Here is my solution.
So, the most important thing to do is read this as posted by Tomalak. It's a really good description of namespaces and easy to understand.
We are going to use XPath to navigate the XML document. Its notation is similar to file systems, where parents and descendants are separated by slashes /. The syntax is explained here, but note that some commands are different for the lxml implementation.
###Problem
Our goal is to extract the city name: the content of <name> which is under <Placemark>. Here's the relevant XML:
<Placemark> <name>CITY NAME</name>
The XPath equivalent to the non-functional code I posted above is:
tree=etree.parse('kml document')
result=tree.xpath('//Placemark/name/text()')
Where the text() part is needed to get the text contained in the location //Placemark/name.
Now this doesn't work, as Tomalak pointed out, cause the name of these two nodes are actually {http://www.opengis.net/kml/2.2}Placemark and {http://www.opengis.net/kml/2.2}name. The part in curly brackets is the default namespace. It does not show up in the actual document (which confused me) but it is defined at the beginning of the XML document like this:
xmlns="http://www.opengis.net/kml/2.2"
###Solution
We can supply namespaces to xpath by setting the namespaces argument:
xpath(X, namespaces={prefix: namespace})
This is easy enough for the namespaces that have actual prefixes, in this document for instance <gx:altitudeMode>relativeToSeaFloor</gx:altitudeMode> where the gx prefix is defined in the document as xmlns:gx="http://www.google.com/kml/ext/2.2".
However, Xpath does not understand what a default namespace is (cf docs). Therefore, we need to trick it, like Tomalak suggested above: We invent a prefix for the default and add it to our search terms. We can just call it kml for instance. This piece of code actually does the trick:
tree.xpath('//kml:Placemark/kml:name/text()', namespaces={"kml":"http://www.opengis.net/kml/2.2"})
The tutorial mentions that there is also an ETXPath method, that works just like Xpath except that one writes the namespaces out in curly brackets instead of defining them in a dictionary. Thus, the input would be of the style {http://www.opengis.net/kml/2.2}Placemark.

python etree with xpath and namespaces with prefix

I can't find info, how to parse my XML with namespace:
I have this xml:
<par:Request xmlns:par="http://somewhere.net/actual">
<par:actual>blabla</par:actual>
<par:documentType>string</par:documentType>
</par:Request>
And tried to parse it:
dom = ET.parse(u'C:\\filepath\\1.xml')
rootxml = dom.getroot()
for subtag in rootxml.xpath(u'//par:actual'):
#do something
print(subtag)
And got exception, because it doesn't know about namespace prefix.
Is there best way to solve that problem, counting that script will not know about file it going to parse and tag is going to search for?
Searching web and stackoverflow I found, that if I will add there:
namespace = {u'par': u"http://somewhere.net/actual"}
for subtag in rootxml.xpath(u'//par:actual', namespaces=namespace):
#do something
print(subtag)
That works. Perfect. But I don't know which XML I will parse, and searching tag (such as //par:actual) is also unknown to my script. So, I need to find way to extract namespace from XML somehow.
I found a lot of ways, how to extract namespace URI, such as:
print(rootxml.tag)
print(rootxml.xpath('namespace-uri(.)'))
print(rootxml.xpath('namespace-uri(/*)'))
But how should I extract prefix to create dictionary which ElementTree wants from me? I don't want to use regular expression monster over xml body to extract prefix, I believe there have to exist supported way for that, isn't it?
And maybe there have to exist some methods for me to extract by ETree namespace from XML as dictionary (as ETree wants!) without hands manipulation?

You cannot rely on the namespace declarations on the root element: there is no guarantee that the declarations will even be there, or that the document will have the same prefix for the same namespace throughout.
Assuming you are going to have some way of passing the tag you want to search (because you say it is not known by your script), you should also provide a way to pass a namespace mapping as well. Or use the James Clark notation, like {http://somewhere.net/actual}actual (the ETXPath has support for this syntax, whereas "normal" xpath does not, but you can also use other methods like .findall() if you don't need full xpath)
If you don't care for the prefix at all, you could also use the local-name() function in xpath, eg. //*[local-name()="actual"] (but you won't be "really" sure it's the right "actual")

Oh, I found it.
After we do that:
dom = ET.parse(u'C:\\filepath\\1.xml')
rootxml = dom.getroot()
Object rootxml contains dictionary nsmap, which contains all namespaces that I want.
So, simplest solution I've found:
dom = ET.parse(u'C:\\filepath\\1.xml')
rootxml = dom.getroot()
nss = rootxml.nsmap
for subtag in rootxml.xpath(u'//par:actual', namespaces=nss):
#do something
print(subtag)
That works.
UPD: that works if user understand what means 'par' in XML he works with. For example, comparing supposed namespace with existing namespace before any other operations.
Still, I like much variant with XPath that understands {...}actual, that was what I tried to achieve.

With Python 3.8.2 I found this question with the same issue.
This is the solution I found, put the namespace in the XPath query. (Between the {})
ApplicationArea = BOD_IN_tree.find('.//ApplicationArea', ns)
if(ApplicationArea is None):
ApplicationArea = BOD_IN_tree.find('.//{http://www.defaultNamespace.com/2}ApplicationArea', ns)
I search for the element without the namespace, then search again if it's not found. I have no control over the inbound documents, some have namespaces, some do not.
I hope this helps!

Parse xbrl file in python

I am working on a xml parser.
The goal is to parse a number of different xml files where prefixes and tags remain consistent but namespaces change.
I am hence trying either:
to parse the xml just by <prefix:tags> without resolving (replacing) the prefix with the namespace. The prefixes remain unchanged from document to document.
to load automatically the namespaces so that the identifier (<prefix:tag>) could be replaced with the proper namespace.
just parse the xml by tag
I have tried with xml.etree.ElementTree.
I also had a look at lxml
I did not find any configuration option of the XMLParser in lxml that could help me out although here I could read an answer where the author suggests that lxml should be able to collect namespaces for me automatically.
Interestingly, parsed_file = etree.XML(file) fails with the error:
lxml.etree.XMLSyntaxError: Start tag expected, '<' not found, line 1, column 1
One example of the files I would like to parse is here

Do not care about ns prefixes, care about complete namespaces
Sometime, people do care about those short prefixes and forgetting, the are of secondary importance. They are only short reference to fully qualified namespace. E.g.
xmlns:trw="http://www.trw.com/20131231"
in xml means, from now on, the "trw:" stands for fully qualified namespace "http://www.trw.com/20131231". Note, that this prefix can be redefined to any other namespace in any following element and may get completely different meaning.
On the other hand, when you care about real meaning, what means here fully qualified namespace, you may think of "trw:row" as "{http://www.trw.com/20131231}row". This translated meaning will be reliable and will not change with prefix changes.
Parsing referred xml
The link to http://edgar.sec.gov/Archives/edgar/data/1267097/000104746914000925/trw-20131231.xml leads to an xml, which validates by xmlstarlet and which lxml is able to parse.
The error message you show is referring to very first character of the stream, so chances are you either met BOM byte in your file, or you are trying to read xml, which is gzipped and shall be decompressed first.
lxml and namespaces
lxml works with namespaces well. It allows you to use XPath expressions, which use namespaces. With controlling namspace prefix on output it is a bit more complex, as it is dependent on xmlns attributes, which are part of serialized document. If you want to modify the prefixes, you must somehow organize these xmlns attributes, often by moving all of the to the root element. At the same time, lxml keeps track of fully qualified namespace of each element, so at the moment of serialization, it will respect this full name as well as currently valid prefix for this namespace.
Handling these xmlna attributes is a bit of more code, refer to lxml documentation.

items = tree.xpath("*[local-name(.) = 'a_tag_goes_here']")
did the job. On top of that I had to browse the generated list items manually to define my other desired filtering functions.

Python: Avoid DTD validation with LXML

I am parsing USPTO patents from 2001 in SGML format. At top of each file, an external DTD is referenced. Unfortunately, this DTD seems to be invalid. A validity check confirms that:
Line 361
Error: A '(' character or an element type is required within declaration of element type "ADR".
<!ELEMENT ADR - - (OMC?,STR*,CITY?,CNTY?,STATE?,CTRY?,PCODE?,EAD*,TEL*,FAX* ...
However, I do not need to validate the SGML files to be processed. I just need the SGML parser to be aware of the entities. Currently, I am using Python with the LXML library. I call the XMLParser as follows:
parser = etree.XMLParser(target=SimpleXMLHandler(), resolve_entities=False, load_dtd=dtd, dtd_validation=False, recover=True)
But still, I am getting immediately the error that the external DTD is invalid in line 361. How can I avoid that issue? I am not the implementor of the DTD, so I am not willing to repair it.
Regards!

As Chrono Kitsune already noted: the problem lies with xml versus sgml: the DTD is not a correct xml dtd, because it is an sgml dtd.
I'd suggest converting the sgml documents to xml first, for example using sx.