If any potential issues using xpath find/update xml tag text

Question

I wrote a script, based on some of the existing StackOverflow questions, but no one perfectly fit my issues. The user use xpath to find a XML tag from a given XML file, and update the tag text based on user inputs. Below is my script using Python 3 (The most difficult part for me is around the namespaces):

import xml.etree.ElementTree as ET
import sys

# user inputs and variables
filename = 'actors.xml'
xpath = 'actor/name'
value = 'test name'
temp_namespace = 'temp_namespace'
    
# get all namespaces    
all_namespaces = dict([node for _, node in ET.iterparse(filename, events=['start-ns'])])

# register namespace
for key in all_namespaces.keys():
    ET.register_namespace(key, all_namespaces[key])

# remove all namespace from elements first
# and temp save it to tag attribute
# The below logic is copied from other Stackoverflow answers
# From **Python 3.8**, we can add the parser to insert comments
it = ET.iterparse(filename, parser=ET.XMLParser(target=ET.TreeBuilder(insert_comments=True)))
for _, el in it:
    prefix, has_namespace, postfix = el.tag.partition('}')
    if has_namespace:
        el.tag = postfix
        el.set(temp_namespace, prefix + has_namespace)

# find and update
root = it.root
for el in root.findall(xpath):
    el.text = str(value)

# get xml comments before root level
doc_comments = []
with open(filename, 'r') as f:
    lines = f.readlines()
    for line in lines:
        if line.startswith('<?xml'):
            continue
        if line.startswith('<' + root.tag):
            break
        else:
            doc_comments.append(line)

def add_tag_namespace(el):
    for sub_el in el:
        if temp_namespace in sub_el.attrib.keys():
            sub_el.tag = sub_el.attrib[temp_namespace] + sub_el.tag
            del sub_el.attrib[temp_namespace]
        add_tag_namespace(sub_el)
    if temp_namespace in el.attrib.keys():
        el.tag = el.attrib[temp_namespace] + el.tag
        del el.attrib[temp_namespace]

# add all namespace back 
# and delete the temp namespace attribute         
add_tag_namespace(root)

# write back to xml file        
tree = ET.ElementTree(root) 
tree.write(filename, encoding='unicode', xml_declaration=True)

if len(doc_comments) == 0:
    sys.exit()

# write xml comments before root back
lines = []
# first read all lines
with open(filename, 'r') as f:
    lines = f.readlines()
# second, insert xml comments back into memory
for i, line in enumerate(lines):
    if line.startswith('<?xml'):            
        insert_at = i + 1
        for comment in doc_comments:
            lines.insert(insert_at, comment)
            insert_at += 1
        break
# finally, write all contents to file
with open(filename, 'w') as f:
    for line in lines:
        f.write(line)

      

actors.xml:

<?xml version="1.0"?>
<actors xmlns:fictional="http://characters.example.com"
        xmlns="http://people.example.com">
    <actor>
        <name>John Cleese</name>
        <fictional:character>Lancelot</fictional:character>
        <fictional:character>Archie Leach</fictional:character>
    </actor>
    <actor>
        <name>Eric Idle</name>
        <fictional:character>Sir Robin</fictional:character>
        <fictional:character>Gunther</fictional:character>
        <fictional:character>Commander Clement</fictional:character>
    </actor>
</actors>