RegEx - matching numbers only in select regions (JS RegEx vs Python PCRE)

gistfile1.py

#author: lo sauer 2011 - lsauer.com
#demonstrating the difference in RegEx engines

Python:
import re
a="123 test 42 <!-- comment 345 commentEnd --> 678 test2 348"
filter(None, re.findall('(?:\<\!--.+\d+.+--\>)|(\d+)',a))

#With RegEx lookbehinds; for demonstration only - not very practical (slow!)
re.findall('(\d+)(?!(?:[^<]+|<(?!!--))*-->)',a))
>>>['123', '42', '678', '2', '348']

JS:
#JS has no lookbehinds; (?:..) is not captured due to the global flag being set
a="123 test 42 <!-- comment 345 commentEnd --> 678 test2 348"
a.match(/(?:\<\!--.+\d+.+--\>)|(\d+)/g)
>>>["123", "42", "<!-- comment 345 commentEnd -->", "678", "2", "348"]
a.match(/(?=\<\!--.+\d+.+--\>)|(\d+)/g)
>>>["123", "42", "", "345", "678", "2", "348"]
a.match(/(?=\<\!--.+\d+.+--\>)|(\d+)/g).filter(Number)
>>>["123", "42", "345", "678", "2", "348"]