[lxml] Somne newby questions on lxml

Feb. 19, 2017

      I'd search the archives for answers to these questions (and to know 
it the broken links are already reported) but the links to the archive site 
appear to be broken (and a google search didn't do much better) on both the

http://lxml.de/3.4/ and https://mailman-mail5.webfaction.com/listinfo/lxml

web pages. That said, I'm new to both python and lxml and mostly new to xml/svg
too. I've been fighting with the perl bindings to the libxml2 C library without
much success, so I decided to see what python had to offer. I'm trying to make
changes to the svg file output from Inkscape so I need to read the svg, make 
changes (which I have figured out how to do in perl) and then write the file 
back out. That all works in perl except pretty printing is broken. In python, 
I can somewhat make pretty printing work, but am struggling with the output 
file. Using this (partial here, fed the complete file to the script) svg file 
as input:

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<svg
   xmlns:dc="http://purl.org/dc/elements/1.1/"
   xmlns:cc="http://creativecommons.org/ns#"
   xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
   xmlns:svg="http://www.w3.org/2000/svg"
   xmlns="http://www.w3.org/2000/svg"
   id="svg"
   enable-background="new 0 0 22.484 43.997"
   xml:space="preserve"
   height="0.80000007in"
   viewBox="0 0 71.999791 57.600007"
   width="1in"
   version="1.1"
   docname="Ammeter_4wire_led_1_schematic.svg"
   y="0"
   x="0"
   gorn="0"><metadata
     id="metadata3411"><rdf:RDF><cc:Work
         rdf:about=""><dc:format>image/svg+xml</dc:format><dc:type
           rdf:resource="http://purl.org/dc/dcmitype/StillImage" /><dc:title></dc:title></cc:Work></rdf:RDF>
...

in to this python script (under cygwin on Windows). I removed the user land
pretty printing function that will actually pretty print the bulk of the svg
code after the name space stuff:

#!/usr/bin/python

# A python xml pretty_print script (which works on svg files unlike the
# builtin version!).

# Import os and sys to get file rename and the argv stuff

import os,sys

# and the lxml library for the xml

from lxml import etree

# Start of the main script

if len(sys.argv) < 2:

    # No input file so print a usage message and exit.

    s = str(sys.argv[0]) + ': Usage: ' + str(sys.argv[0]) + ' xml_file'
    print s
    sys.exit()

# Parse the xml document

try:

    file = sys.argv[1]

    parser = etree.XMLParser(remove_blank_text=True)

    doc = etree.parse(file)

except IOError:

    print 'Error: can\'t find or read file ' + file
    sys.exit()

else:

    doc.write(sys.stdout, pretty_print=True)

#   doc.write(sys.stdout, xml_declaration=True, encoding="UTF-8", standalone=False, pretty_print=True)

    sys.exit()

produces this output:

<svg xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:cc="http://creativecommons.org/ns#" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:svg="http://www.w3.org/2000/svg" xmlns="http://www.w3.org/2000/svg" id="svg" enable-background="new 0 0 22.484 43.997" xml:space="preserve" height="0.80000007in" viewBox="0 0 71.999791 57.600007" width="1in" version="1.1" docname="Ammeter_4wire_led_1_schematic.svg" y="0" x="0" gorn="0">
  <metadata id="metadata3411">
    <rdf:RDF>
      <cc:Work rdf:about="">
        <dc:format>image/svg+xml</dc:format>
        <dc:type rdf:resource="http://purl.org/dc/dcmitype/StillImage"/>
        <dc:title/>
      </cc:Work>
    </rdf:RDF>

There are two things wrong here: first the 

<?xml version="1.0" encoding="UTF-8" standalone="no"?>

line is missing in the output. I have figured out that it can be added via the 
commented out output statement in the python code as long as I know (or assume
I know) what the encoding was, but I would prefer to copy the values from the
input line through (which is what the perl bindings do). Is there a way to do 
that that I'm not finding?
	Then the pretty printing has failed on the name space xml at the top of
the file (possibly because I haven't done something necessary to register the
name spaces?) I'm first looking to be able to read in and write out (without 
making any changes) the svg file so I know at least that works before I start
changing things but am not having much luck at it. There are almost no examples
that google can find of code that does this (I found the output paramters in
the svgutils package on github which uses lxml, but he too is assuming he knows
what the encoding is, and doesn't copy the input settings). Can anyone suggest 
a solution or point me at documentation or preferably examples of how it is 
done (or at a more suitable mailing list if this isn't it)?

Peter Van Epp