Python replace using regex

Question

Does anyone know how to replace all ocurences of '<\d+' regex with '\r\n<\d+', for example

"<20"

should be transformed to

"\r\n<20"

but

"> HELLO < asassdsa"

shuld be untouched

Answer 1

>>> import re
>>> str = "<20"
>>> output = re.sub(r'<(?=\d)', r'\r\n<', str)
>>> output
'\r\n<20'

Answer 2

import re
def replace(value):
  return re.sub(r'(<\d)', r'\r\n\1', value)

Or using lookahead:

import re
def replace(value):
  return re.sub(r'(?=<\d)', r'\r\n', value)