Python replace function [replace once]

Solution 1:

I'd probably use a regex here:

>>> import re
>>> s = "The scary ghost ordered an expensive steak"
>>> sub_dict = {'ghost':'steak','steak':'ghost'}
>>> regex = '|'.join(sub_dict)
>>> re.sub(regex, lambda m: sub_dict[m.group()], s)
'The scary steak ordered an expensive ghost'

Or, as a function which you can copy/paste:

import re
def word_replace(replace_dict,s):
    regex = '|'.join(replace_dict)
    return re.sub(regex, lambda m: replace_dict[m.group()], s)

Basically, I create a mapping of words that I want to replace with other words (sub_dict). I can create a regular expression from that mapping. In this case, the regular expression is "steak|ghost" (or "ghost|steak" -- order doesn't matter) and the regex engine does the rest of the work of finding non-overlapping sequences and replacing them accordingly.

Some possibly useful modifications

• regex = '|'.join(map(re.escape,replace_dict)) -- Allows the regular expressions to have special regular expression syntax in them (like parenthesis). This escapes the special characters to make the regular expressions match the literal text.
• regex = '|'.join(r'\b{0}\b'.format(x) for x in replace_dict) -- make sure that we don't match if one of our words is a substring in another word. In other words, change he to she but not the to tshe.

Solution 2:

Split the string by one of the targets, do the replace, and put the whole thing back together.

pieces = s.split('steak')
s = 'ghost'.join(piece.replace('ghost', 'steak') for piece in pieces)

This works exactly as .replace() would, including ignoring word boundaries. So it will turn "steak ghosts" into "ghost steaks".

Solution 3:

Rename one of the words to a temp value that doesn't occur in the text. Note this wouldn't be the most efficient way for a very large text. For that a re.sub might be more appropriate.

 s="The scary ghost ordered an expensive steak"
 print s
 s=s.replace("steak","temp")
 s=s.replace("ghost","steak")
 S=s.replace("temp","steak")
 print s

Solution 4:

Use the count variable in the string.replace() method. So using your code, you wouold have:

s="The scary ghost ordered an expensive steak"
print s
s=s.replace("steak","ghost", 1)
s=s.replace("ghost","steak", 1)
print s

http://docs.python.org/2/library/stdtypes.html