I wanted to replace string matches with the output of piped shell commands

replace_text.py

# python
import subprocess
import re

o    = open("some_html_file.out.html","w")
data = open("./some_html_file.html").read()

def gen_id(match):
  match = match.group()
  id    = subprocess.getoutput("cat /dev/urandom | env LC_CTYPE=C tr -cd 'a-f0-9' | head -c 4")
  return f'{match} id="{id}"'

o.write(re.sub(r'(<p)', gen_id, data))
o.close()
print('done')