String Replace only if whole word?

Michael Yanowitz m.yanowitz at
Fri Nov 17 16:43:10 CET 2006

>Michael Yanowitz wrote:
>> Hello:
>>   I am hoping someone knows if there is an easier way to do this or
>> already implemented something that does this, rather than reinventing the
>> wheel:
>>   I have been using the string.replace(from_string, to_string,
>> to replace names in a file with their IP address.
>>   For example, I have definitions file, that looks something like:
>>   ALTIMETER_100
>> SIB
>>  WIN2000
>>   and I have a text file (a Python script) that has these names in the
>> In most cases the string.replace() command works great. But there is one
>> instance which it fails:
>> Suppose I had in the file:
>>  if (LAPTOP_IS_UP()):
>>    It would replace the string with:
>>  if (""_IS_UP()):
>>    Is there any easy way to avoid this, only replace if a whole word
>> matches?
>> I probably need something which determines when a word ends, and I will
>> define
>>  a word as containing only 'A'-'Z','a'-'z','0'-'9','_' . As long as the
>> string
>> contains more of the word digits after the match, don't replace?
>> Thanks in advance:
>> Michael Yanowitz
>You need regular expressions for this. Use the re module.
>from the docs:
>re.sub(pattern, repl, string[, count])
>Return the string obtained by replacing the leftmost non-overlapping
>occurrences of pattern in string by the replacement repl.
>Your pattern would be "[^A-Za-z0-9_]word[^A-Za-z0-9_]"
>[^xy] is approximately not in ('x', 'y')
>Juho Schultz

  This works great except for one thing:

The character after the replacement is deleted, so that if I have
     send_data (LAPTOP, test_string)
    it would replace it with:
     send_data ( test_string)
  (ignoring that the is not quoted). The comma is missing.

Thanks in advance:
Michael Yanowitz

More information about the Python-list mailing list