They are compatible for the most part. There are some differences, though, apart from the different syntax (/regex/ in PHP vs. re.compile(r"regex") in Python):

1. PCRE supports \Q...E to escape metacharacters, Python doesn't.
2. PCRE supports \cA-\cZ control character matching, Python doesn't.
3. Hyphen in [\d-z] or [a-\d] is a literal in PHP, not in Python.
4. PCRE supports \z (end-of-string), Python doesn't, only \Z (end-of-string before optional final linefeed).
5. \b will match word boundaries only around ASCII characters in PCRE, in Python it can match locale-dependently if the option is set.
6. You can refer to \1 etc. backreferences ahead of their capturing parentheses in PCRE, you can't in Python.
7. You can't turn off mode modifiers within the regex ((?-s) etc.) in Python.
8. You don't get atomic grouping (?>...) or possessive quantifiers (.++) in Python, only in PCRE.
9. Lookbehind can be finite-length in PCRE, must be fixed-length in Python.
10. There is no \G pattern (location of previous match).
11. No conditional matching in Python, only in PCRE: (?(?=regex)then|else).
12. No \x1234 for Unicode code points matching in Python. No p{L} and other Unicode property matching, either. In PHP, it depends how it's configured/compiled.
13. No [:alpha:] POSIX character classes in Python.

Collected from regular-expressions.info, leaving out some of the more esoteric stuff. But not much.

Moral: Buy RegexBuddy and use it to translate the regexes for you.

I would suggest that using a regex for decimal range validation is not necessarily the correct answer for this problem. This is far more readable:

def valid_ip(s):
    m = re.match(r"(\d+)\.(\d+)\.(\d+)\.(\d+)$", s)
    if m is None:
        return False
    parts = [int(m.group(1+x)) for x in range(4)]
    if max(parts) > 255:
        return False
    return True

I'm not sure of any software that would do that, however, regex101.com allows you to switch languages.

You can write a PERL regex by choosing pcre (php) from the FLAVOR menu and then switch to Python by selecting python from the same list.

If it doesn't work with python, you'll be able to tell and can then start removing parts of the regex until it works and start from there.

Here is a demo showing how the regex works in PERL, but when you switch it to python, it doesn't match. (Because python doesn't support the horizontal whitespace character \h.)

https://regex101.com/r/1lCSHV/1

So, you could change the \h to \s and it will now work.

Working version .. display all images from a given web site using tag IMG src > code:

  import re
  import urllib
  print "Start"
  url="http://www.deviantart.com"
  data=urllib.urlopen(url)
  out=data.read()
  print 
  title_regex = "/<title>(.+)<\/title>/i"
  m = re.search("<title>(.+)<\/title>", out)
  print "first",m
  print "grop",m.group(1)

  title_regex = "/<title>(.+)<\/title>/i"

  pics = re.compile(r"<IMG[^>]*src=([^>]*[^/])")#Change IMG tag 
  allpics=pics.findall(out)
  print "found",pics
  for mypic in allpics:
     print "< IMG src=",mypic

thanks all

PCRE (including preg_match_all) requires a pattern boundary. You need to wrap the entire pattern in /, @, #, %, or many other possible options. I suggest % as it doesn't look like you are using it in either pattern, that is:

%(?:\* ([\w\d\(\),\.\'\"\-\:#|/ ]+)|(?<= @)(\w+)(?: (.+))?)%