Cannot write XML file with default namespace

Question

I'm writing a Python script to update Visual Studio project files. They look like this:

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="4.0" DefaultTargets="Build" 
      xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <PropertyGroup>
      ...

The following code reads and then writes the file:

import xml.etree.ElementTree as ET

tree = ET.parse(projectFile)
root = tree.getroot()
tree.write(projectFile,
           xml_declaration = True,
           encoding = 'utf-8',
           method = 'xml',
           default_namespace = "http://schemas.microsoft.com/developer/msbuild/2003")

Python throws an error at the last line, saying:

ValueError: cannot use non-qualified names with default_namespace option

This is surprising since I'm just reading and writing, with no editing in between. Visual Studio refuses to load XML files without a default namespace, so omitting it is not optional.

Why does this error occur? Suggestions or alternatives welcome.

Answer 1

This is a duplicate to Saving XML files using ElementTree

The solution is to define your default namespace BEFORE parsing the project file.

ET.register_namespace('',"http://schemas.microsoft.com/developer/msbuild/2003")

Then write out your file as

tree.write(projectFile,
           xml_declaration = True,
           encoding = 'utf-8',
           method = 'xml')

You have successfully round-tripped your file. And avoided the creation of ns0 tags everywhere.