Find and replace in a file with regular expression

[Wolfgang Grafen]

Just in case you didn't think about it there is a plain replace method for strings

How to quick-search this method with 'dir'
 >>> dir("")
['__add__', '__class__', '__contains__', '__delattr__', '__doc__', '__eq__', '__ge__', '__getattribute__', '__getitem__', '__getnewargs__', '__getslice__', '__gt__', '__hash__', '__init__', '__le__', '__len__', '__lt__', '__mod__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', 
'__repr__', '__rmod__', '__rmul__', '__setattr__', '__str__', 'capitalize', 'center', 'count', 'decode', 'encode', 'endswith', 'expandtabs', 'find', 'index', 'isalnum', 'isalpha', 'isdigit', 'islower', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'replace', 'rfind', 'rindex', 
'rjust', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill']

 >>> help("".replace)
Help on built-in function replace:

replace(...)
     S.replace (old, new[, maxsplit]) -> string

     Return a copy of string S with all occurrences of substring
     old replaced by new.  If the optional argument maxsplit is
     given, only the first maxsplit occurrences are replaced.

and now how to apply it:
new_text = open(fileName).read().replace("SOURCE", "REPLACE")

which is the preferred method for a simple task like this.

TOXiC wrote:
> Hi everyone,
> First I say that I serched and tryed everything but I cannot figure 
> out how I can do it.
> I want to open a a file (not necessary a txt) and find and replace a 
> string.
> I can do it with:
> 
> import fileinput, string, sys
> fileQuery = "Text.txt"
> sourceText = '''SOURCE'''
> replaceText = '''REPLACE'''
> def replace(fileName, sourceText, replaceText):

Now how to solve it with a simple regular expression:

 >>> import re
 >>> re_replace = re.compile("SOURCE").sub
 >>>
 >>> txt = "   SOURCE   SOURCE \n   SOURCE  "
 >>>
 >>> print re_replace("REPLACE", txt)
'   REPLACE   REPLACE \n   REPLACE  '
 >>> new_text = re_replace("REPLACE", open(fileName).read())

A regular expression for this task is kind of overkill. Mastering
regular expression is the efford very worth.

Wolfgang Grafen