Multiple replacements (was: The fundamentals...)

[Simon Brunning]

> From:	mspiggie at my-deja.com [SMTP:mspiggie at my-deja.com]
> I have been trying to find a way to use replace() to perform more than
> one replacement within a given file.  For instance, suppose I needed to
> replace ". " with "\n", but also need to replace "!" with "exclamation"
> and "?" with "question".  I have tried several approaches to this, but
> none of my neophyte ideas have produced satisfying results.
 
Some time ago, /F gave me this:

class MultiReplace:
    def __init__(self, replacements, wholeWords=None, caseInsensitive=None):
        self.wholeWords = wholeWords
        self.charMap = None
        self.replacements = replacements
        
        # Assume char to char mapping...
        if not wholeWords:
            charMap = map(chr, range(256))
            for fromVal, toVal in replacements.items():
                if len(fromVal) <> 1 or len(toVal) <> 1:
                    break
                if caseInsensitive:
                    charMap[ord(fromVal.upper())] = toVal
                    charMap[ord(fromVal.lower())] = toVal
                else:
                    charMap[ord(fromVal)] = toVal
            else:
                self.charMap = "".join(charMap)
                return

        # String to string mapping - use a regular expression        
        fromVals = replacements.keys()
        fromVals.sort() # lexical order

        if not wholeWords: # Build re pattern
            rePattern = '|'.join(map(re.escape, fromVals))
        else:
            rePattern = r'\b(' + '|'.join(map(re.escape, fromVals)) + r')\b'
        
        if caseInsensitive: # Compile re
            self.rePattern = re.compile(rePattern, re.I)
        else:
            self.rePattern = re.compile(rePattern)

    def replace(self, string):
        # apply replacement to string
        
        if self.charMap: # Char to char mapping
            return string.translate(self.charMap)

        # String to string mapping        
        return self.rePattern.sub(self.__replaceInMatch, string)
    
    def __replaceInMatch(self, match):
        item = match.group(0)
        return self.replacements.get(item, item)

I have made some changes to it since /F gave it to me, so if it's crap my,
it's my fault. ;-)

Use it like this:

>>>import MultiReplace
>>>replaceDict = {'a': 'b', 'c': 'd'} # From and to values in this
dictionary - strings can be longer than 1 character if you want.
>>>multiReplace = MultiReplace.MultiReplace(replaceDict)
>>>replace('spam')
'spbm'

Cheers,
Simon Brunning
TriSystems Ltd.
sbrunning at trisystems.co.uk
Are you going to come quietly, or do I have to use earplugs? - from The Goon
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