python中的正则表达式：是否可以获得匹配，替换和最终字符串？

Question

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

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

There are three things that the regex engine finds that are of interest to me:

• The matched string
• The replacement string
• The final processed string

When using re.sub , the final string is what's returned. But is it possible to access the other two things, the matched string and replacement string?

Here's an example:

orig = "This is the original string."
matchpat = "(orig.*?l)"
replacepat = "not the \\1"

final = re.sub(matchpat, replacepat, orig)
print(final)
# This is the not the original string

The match string is "original" and the replacement string is "not the original" . Is there a way to get them? I'm writing a script to to search and replace in many files, and I want it to print it what it's finding and replacing, without printing out the entire line.

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 @FJ 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]

Answer 2

I looked at the documentation and it seems like you can pass a function reference into the re.sub :

import re

def re_sub_verbose(pattern, replace, string):
  def substitute(match):
    print 'Matched:', match.group(0)
    print 'Replacing with:', match.expand(replace)

    return match.expand(replace)

  result = re.sub(pattern, substitute, string)
  print 'Final string:', result

  return result

And I get this output when running re_sub_verbose("(orig.*?l)", "not the \\\\1", "This is the original string.") :

Matched: original
Replacing with: not the original
This is the not the original string.