Develop Reference

Checking if XML declaration is present

I am trying to check whether an xml file contains the necessary xml declaration ("header"), let's say:
<?xml version="1.0" encoding="UTF-8"?>
...rest of xml file...
I am using xml ElementTree for reading and getting info out of the file, but it seems to load a file just fine even if it does not have the header.
What I tried so far is this:
import xml.etree.ElementTree as ET
tree = ET.parse(someXmlFile)
try:
xmlFile = ET.tostring(tree.getroot(), encoding='utf8').decode('utf8')
except:
sys.stderr.write("Wrong xml2 header\n")
exit(31)
if re.match(r"^\s*<\?xml version=\'1\.0\' encoding=\'utf8\'\?>\s+", xmlFile) is None:
sys.stderr.write("Wrong xml1 header\n")
exit(31)
But the ET.tostring() function just "makes up" a header if it is not present in the file.
Is there any way to check for a xml header with ET? Or somehow throw an error while loading the file with ET.parse, if a file does not contain the xml header?

tl;dr
from xml.dom.minidom import parseString
def has_xml_declaration(xml):
return parseString(xml).version
From Wikipedia's XML declaration
If an XML document lacks encoding specification, an XML parser assumes
that the encoding is UTF-8 or UTF-16, unless the encoding has already
been determined by a higher protocol.
...
The declaration may be optionally omitted because it declares as its
encoding the default encoding. However, if the document instead makes
use of XML 1.1 or another character encoding, a declaration is
necessary. Internet Explorer prior to version 7 enters quirks mode, if
it encounters an XML declaration in a document served as text/html
So even if the XML declaration is omitted in an XML document, the code-snippet:
if re.match(r"^<\?xml\s*version=\'1\.0\' encoding=\'utf8\'\s*\?>", xmlFile.decode('utf-8')) is None:
will find "the" default XML declaration in this XML document. Please note, that I have used xmlFile.decode('utf-8') instead of xmlFile.
If you don't worry to use minidom, you can use the following code-snippet:
from xml.dom.minidom import parse
dom = parse('bookstore-003.xml')
print('<?xml version="{}" encoding="{}"?>'.format(dom.version, dom.encoding))
Here is a working fiddle
Int bookstore-001.xml an XML declaration ist present, in bookstore-002.xml no XML declaration ist present and in bookstore-003.xml a different XML declaration than in the first example ist present. The print instruction prints accordingly the version and the encoding:
<?xml version="1.0" encoding="UTF-8"?>
<?xml version="None" encoding="None"?>
<?xml version="1.0" encoding="ISO-8859-1"?>

How to output elements in ElementTree PIParser?

If you want to preserve comments in an XML file with ElementTree, you can use the PIParser from http://effbot.org/zone/element-pi.htm
So if I have a file containing
<?xml version="1.0" encoding="iso-8859-1"?>
<!-- This is a comment -->
<root>
<foo>Hello World</foo>
</root>
<!-- That's all, folks -->
then the two comments will be preserved.
PIParser wraps the xml in another <document> node, so there is something to contain any comments that come outside the root node. The two comments are just two more elements contained in <document>.
But then how should I output the xml? I use code like this to output the contents of <document> without outputting the <document> tag itself:
file.write('<?xml version="1.0" encoding="%s"?>\n' % encoding)
doc = tree.getroot()
for child in doc:
file.write(ET.tostring(child, encoding, method))
file.write("\n")
Now, that seems to work if encoding is "utf-8". The tostring() method does not output one of those <?xml...?> lines, presumably because utf-8 is the default. That's why I wrote the <?xml...?> explicitly with file.write() above. But if encoding is "iso-8859-1" then tostring() puts a <?xml version="1.0" encoding="iso-8859-1"?> at the start of every element for which it is called! So I get one in front of every comment outside the root node, and another in front of the root node itself. I don't want that, I only want one at the top of the file. But instead of getting the xml as shown above, I get
<?xml version="1.0" encoding="iso-8859-1"?>
<?xml version='1.0' encoding='iso-8859-1'?>
<!-- This is a comment -->
<?xml version='1.0' encoding='iso-8859-1'?>
<root>
<foo>Hello World</foo>
</root>
<?xml version='1.0' encoding='iso-8859-1'?>
<!-- That's all, folks -->
How do I control whether tostring() outputs a <?xml...?>? Or, should I be doing this another way?

copying input xml file and write exactly with Python

Input xml file:
<?xml version="1.0"?>
<res:testcases xmlns:res="urn:testcases" id="a1e4bfdb-40a2-485c-a1ac-54d220056dd5" type="MODEL">
<mode>PRESSURE_CONTROL</mode>
<category>ADULT</category>
<testcase id="1" type="UNIQUE">
<parameter id="PEEP" value="1.0">true</parameter>
<parameter id="CMV_FREQ" value="4.0">true</parameter>
<parameter id="PRESS_ABOVE_PEEP" value="0.0">true</parameter>
<parameter id="I_E_RATIO" value="0.1">false</parameter>
</testcase>
</res:testcases>
Python Code:
import xml.etree.ElementTree as ET
tree = ET.parse('/home/AlAhAb65/Desktop/input.xml')
root = tree.getroot()
root.attrib['type'] = 'AVA'
tree.write('/home/AlAhAb65/Desktop/output1.xml')
Output xml file:
<ns0:testcases id="a1e4bfdb-40a2-485c-a1ac-54d220056dd5" type="AVA" xmlns:ns0="urn:testcases">
<mode>PRESSURE_CONTROL</mode>
<category>ADULT</category>
<testcase id="1" type="UNIQUE">
<parameter id="PEEP" value="1.0">true</parameter>
<parameter id="CMV_FREQ" value="4.0">true</parameter>
<parameter id="PRESS_ABOVE_PEEP" value="0.0">true</parameter>
<parameter id="I_E_RATIO" value="0.1">false</parameter>
</testcase>
</ns0:testcases>
The problem is when I am copying and writing the output xml file 3 unexpected things happen. They are given below:
1. The first line from the input xml file is removed automatically
2. In second line (in input), the text 'res' is replaced with 'ns0'. Same happens while closing the tag
3. The order of the attribute (of the second line of input) is changed.
But I want to write (as output) the exact copy of xml file that I got as an input. Please help me in this regard.

W3 has defined a Canonical XML standard. Documents written in this format can be faithfully round-tripped by any C14N-compliant toolchain.
In the case of lxml.etree (a more capable implementation of the ElementTree API with C14N support), this means that you need to do two things:
Convert your original input document into C14N form.
Use the ElementTree.write_c14n() call to generate your output document.
A C14N-form version of your input file will look like so (generated by the xmlstarlet c14n command):
<res:testcases xmlns:res="urn:testcases" id="a1e4bfdb-40a2-485c-a1ac-54d220056dd5" type="MODEL">
<mode>PRESSURE_CONTROL</mode>
<category>ADULT</category>
<testcase id="1" type="UNIQUE">
<parameter id="PEEP" value="1.0">true</parameter>
<parameter id="CMV_FREQ" value="4.0">true</parameter>
<parameter id="PRESS_ABOVE_PEEP" value="0.0">true</parameter>
<parameter id="I_E_RATIO" value="0.1">false</parameter>
</testcase>
</res:testcases>
...and an appropriately modified version of your code:
#!/usr/bin/env python
import lxml.etree
tree = lxml.etree.parse('input.xml')
root = tree.getroot()
root.attrib['type'] = 'AVA'
tree.write_c14n('output1.xml')
If you add an XML declaration (the <?xml version="1.0"?> line), you will be noncomplaint with the C14N standard. As such, this is something you absolutely should not do. If you really, really want to do this wrongheaded thing...
Don't.
But if you must, you'd do it like so:
outfile = open('output1.xml', 'w')
outfile.write('<?xml version="1.0"?>\n')
tree.write_c14n(outfile)
outfile.close()

From the documentation page, the XML declaration can be added like this:
tree.write('/home/AlAhAb65/Desktop/output1.xml', xml_declaration=True)
You should also add the encoding because the default one is us-ascii:
tree.write('/home/AlAhAb65/Desktop/output1.xml', encoding='utf-8', xml_declaration=True)
Or you can retrieve the encoding from the original file, but in any case you will get a different XML declaration, probably something like this:
<?xml version="1.0" encoding="UTF-8"?>
Or you can manually add the XML declaration. Anyway a slight declaration mismatch should not be a problem for any robust XML parser as long as the declared encoding is coherent with the real encoding.
Attribute order is not significant in XML, so the information is probably lost when the file is parsed within the API. There is probably no simple way to make this work when processing the file through the standard ElementTree API. You would probably better have to go with lxml C14N support if you want to do minor changes to the file.
The namespace prefixes are changed by default in ElementTree. To prevent this behavior, you can switch to lxml which seems to preserve namespace prefixes by default:
Because etree is built on top of libxml2, which is namespace prefix aware, etree preserves namespaces declarations and prefixes while ElementTree tends to come up with its own prefixes (ns0, ns1, etc). When no namespace prefix is given, however, etree creates ElementTree style prefixes as well.
Switching to lxml is a good idea in any case, but the changes you observe should not be a problem if the program reading the file at the other end is XML compliant enough. Unfortunately a lot of XPath processors have issues with namespace prefixes changes...

<?xml version=“1.0” encoding=“UTF-8”?> not <?xml version='1.0' encoding='UTF-8'?>

I am using lxml with
tree.write(xmlFileOut, pretty_print = True, xml_declaration = True, encoding='UTF-8'
to write out my opened and edited xml file, but I absolutely need to have the xml declaration as
<?xml version=“1.0” encoding=“UTF-8”?>
and NOT
<?xml version='1.0' encoding='UTF-8'?>
Now I know they are exactly the same when it comes to xml, but I am dealing with a very tricky customer who absolutely has to have " in the declaration and not '. I have searched everywhere but can't find the answer.
Could I create it and add it in myself to the head of the xml somehow?
Could I tell lxml that this is what I need as an xml declaration?

This is a site for coding questions, not a site for advice in dealing with tricky customers. Your customer is wrong; your problem is political/commercial, not technical.

Writing XML files with Python

I have created an XML document with the following contents.
<books>
<book id="1">
<title>Title01</title>
<authors/>
<pages>
<page>Page01</page>
<page>Page02</page>
<page>Page03</page>
<page>Page04</page>
<page>Page05</page>
</pages>
</book>
<book id="2">
<title>Title02</title>
<authors/>
<pages>
<page>Page01</page>
<page>Page02</page>
<page>Page03</page>
<page>Page04</page>
<page>Page05</page>
</pages>
</book>
</books>
I then use a Python script to split up and write the individual books into separate files;however, the resulting files are not XML files because they do not have the XML declaration. Is there a way of creating XML files in Python?
The idea is to ensure that each file has the XML declaration as show below.
<?xml version="1.0" encoding="ISO-8859-1" ?>
<book id="1">
<title>Title01</title>
<authors/>
<pages>
<page>Page01</page>
<page>Page02</page>
<page>Page03</page>
<page>Page04</page>
<page>Page05</page>
</pages>
</book>

Why don't you write the xml declaration to each book file before you write the book entry?

Encode your files in UTF-8 instead of some legacy encoding like ISO-8859-1. Then you don't need an XML declaration.

You should look into the xml.etree.ElementTree module. The link is for Python 3, but it was included way before that. I use it in Python 2.5, so you should be ok.
Also, I have had good results with xml.dom.minidom. Once you have built a Document (by adding elements with createElement('ELEM_NAME'), you just write it to a stream with mydoc.toprettyxml().