[Python] How to correctly use escape characters to write a mathematical string to a XML file...

I have an XML file which I am trying to edit using Python. This is an example of the content of the XML file:

<?xml version="1.0" encoding="utf-8"?>
<NEKTAR>
<CONDITIONS>
<FUNCTION NAME="Baseflow">
<E VAR="u0" VALUE="(x>3) * (y <= 3) * 4 * x"/>
</FUNCTION>
</CONDITIONS>
</NEKTAR>


In the original file, the value for u0 is set to 0. Using Python, I want to change this value to the mathematical expression shown in the code-block. I have tried two approaches un-successfully:

1. Write the in-equalities using the escape characters such as &lt; and &gt;
2. Try to use CDATA

What would be the right approach to do something like this using xml.etree.ElementTree ?

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