Regex in python: is it possible to get the match, replacement, and final string?

Question

For doing a regex substitution, there are three things that you give it:

• The match pattern
• The replacement pattern
• The original string
<

Answer 1

class Replacement(object):

    def __init__(self, replacement):
        self.replacement = replacement
        self.matched = None
        self.replaced = None

    def __call__(self, match):
        self.matched = match.group(0)
        self.replaced = match.expand(self.replacement)
        return self.replaced

>>> repl = Replacement('not the \\1')
>>> re.sub('(orig.*?l)', repl, 'This is the original string.')
    'This is the not the original string.'
>>> repl.matched
    'original'
>>> repl.replaced
    'not the original'

---

Edit: as @F.J has pointed out, the above will remember only the last match/replacement. This version handles multiple occurrences:

class Replacement(object):

    def __init__(self, replacement):
        self.replacement = replacement
        self.occurrences = []

    def __call__(self, match):
        matched = match.group(0)
        replaced = match.expand(self.replacement)
        self.occurrences.append((matched, replaced))
        return replaced

>>> repl = Replacement('[\\1]')
>>> re.sub('\s(\d)', repl, '1 2 3')
    '1[2][3]'

>>> for matched, replaced in repl.occurrences:
   ....:     print matched, '=>', replaced
   ....:     
 2 => [2]
 3 => [3]