Thanks @koulesali, you could try the following, which should work.
As well as replacing analytics with window.analytics,
Go to the script provided by segment.
At the start of the script you’ll find this expression:
var analytics=window.analytics=window.analytics||[];
replace it with
var analytics=window.analytics=window.analytics||Object.create(Array.prototype);
This is a bit of hack, but it should work.
It tells Anvil’s Javascript <-> Python bridge to not treat window.analytics as a Python list
Segment does some unconventional overloading of a Javascript Array, which we’re not able to handle when we convert it to a Python list