How to do multiple string replacements in a cleaner manner? - Python

Question

What is a fast way of doing multiple string.replace? I'm trying to add spaces to shorten english words like

he'll -> he 'll
he's -> he 's
we're -> we 're
we've -> we 've

also i'm adding spaces in between before and punctuation as such:

"his majesty" ->  " his majesty " 
his; majesty -> his ; majesty

Is there a faster and cleaner way to do it? It's a little too slow for the purpose but I've been doing it this way:

def removeDoubleSpace(sentence):
  sentence.replace("  ", " ")
  if "  " in sentence:
    removeDoubleSpace(sentence)

def prepro(sentence):
  sentence = sentence.replace(",", " ,")
  sentence = sentence.replace(";", " ; ")
  sentence = sentence.replace(":", " : ")
  sentence = sentence.replace("(", " ( ")
  sentence = sentence.replace("(", " ) ")
  sentence = sentence.replace("‘"," ‘ ")
  sentence = sentence.replace('"',' " ')
  sentence = sentence.replace("'re", " 're")
  sentence = sentence.replace("'s", " 's")
  sentence = sentence.replace("'ll", " 'll")
  sentence = removeDoubleSpace(sentence)
  return sentence

Have you tried using `re.sub()` from the regular expressions module? — Joel Cornett, Oct 03 '12 at 03:36
All those `replace` calls *don't do anything* because they return the modified string (since strings are immutable). — nneonneo, Oct 03 '12 at 04:34

verdesmarald · Accepted Answer · 2012-10-03T03:50:31.173

5

You could use a few regular expressions to accomplish the same task:

import re

# Replace multiple consecutive spaces with a single space
# Example: "One Two  Three    Four!" -> "One Two Three Four!"
sentence = re.sub(' +', ' ', sentence)    

# Surround each instance ; : ( ) ‘ and " with spaces
# Example: '"Hello;(w)o:r‘ld"' -> " Hello ;  ( w ) o : r ‘ ld "
sentence = re.sub('([;:()‘"])', ' \\1 ', sentence)

# Insert a space before each instance of , 's 're and 'll
# Example: "you'll they're, we're" -> "you 'll they 're , we 're"
sentence = re.sub("(,|'s|'re|'ll)", ' \\1', sentence)

return sentence

edited Oct 03 '12 at 03:50

answered Oct 03 '12 at 03:40

verdesmarald

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what does the `' +', ' '` , `\\1 ' mean? would this perform faster than the replace? – alvas Oct 03 '12 at 03:43
1

@2er0 I added some comments, `' +'` matches multiple consecutive spaces. `\\1` in the replacement string inserts the value that was matched between the parentheses (`()`) in the pattern. You would have to test it to see if it's faster, as I don't have access to your test data, but my instinct is yes. – verdesmarald Oct 03 '12 at 03:45
@2ero If this still isn't good enough, you could also loop through the characters in the string and build up the output sequentially in a list, then convert it to a string. However, that approach is painful to code and I would only recommend it if all else fails. I'm also not sure if performance gain would be significant. – verdesmarald Oct 03 '12 at 04:07

How to do multiple string replacements in a cleaner manner? - Python

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