[Python] creating a new column in polars applying a function to a column

I have the following code for manipulating a polars dataframe that does not work

import polars as pl
import xml.etree.ElementTree as ET

# create a sample dataframe
df = pl.DataFrame({
'A': [1, 2, 3],
'B': ['<p>some text</p><p>bla</p>', '<p>some text<p><p>foo</p>', '<p>some text<p>']
})

def func(mystring):
return mystring*2

def func2(xml_string):
root = ET.fromstring(xml_string)
text_list = []
for elem in root.iter():
text = elem.text.strip() if elem.text else ''
text_list.append(text)
return test_list

# create a sample series to add as a new column
df = df.with_columns((pl.col("A").map_batches(lambda x: func(x)).alias('new_col')))
df = df.with_columns((pl.col("B").map_batches(lambda x: func2(x)).alias('new_col2')))

print(df)


The first line for adding a column works, i.e. adding new_col

but the second one does not work.

The error that I get is:

ComputeError: TypeError: a bytes-like object is required, not 'Series'
​

Basically the use case that I have iss that a column contains XML string that I have to manipulate creating a XML object and extracting information.

How can I proceed?

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