Anonymise XML text by XPATH

anon.py

# usage: anon.py input.xml output.xml
import random
import string
import sys

from lxml import etree

XPATHS = [
    '/Path/To/Elements/*',
    '/Another/Path/'
]

TEXT_GROUPS = [
    string.ascii_lowercase,
    string.ascii_uppercase,
    ''.join(str(i) for i in range(0, 10))
]

def anonymise(input):
    output = []
    for char in input:
        for text_group in TEXT_GROUPS:
            if char in text_group:
                output.append(random.choice(text_group))
                break
        else:
            output.append(char)
    return ''.join(output)

def main(input_file, output_file):
    xml = etree.parse(input_file)
    memo = {}
    for xpath in XPATHS:
        for element in xml.iterfind(xpath):
            if element.text:
                if element.text not in memo:
                    memo[element.text] = anonymise(element.text)
                element.text = memo[element.text]
    xml.write(output_file)

if __name__ == '__main__':
    main(*sys.argv[1:])