Python - replace multiline string in a file

Question

I'm writing a script which finds in a file a few lines of text. I wonder how to replace exactly that text with other given (new string might be shorter or longer). I'm using re.compile() to create a multiple line pattern then looking for any match in a file I do like this:

for match in pattern.finditer(text_in_file)
    #if it would be possible I wish to change 
    #text in a file here by (probably) replacing match.group(0)

Is it possible to accomplish in this way (if yes, then how to do it in the easiest way?) or my approach is wrong or hard to do it right (if yes, then how to do it right?)

Use re.sub not re.finditer.

Ashwini Chaudhary
– Ashwini Chaudhary

2014-01-22 16:43:36 +00:00
Commented Jan 22, 2014 at 16:43 — Ashwini Chaudhary
– Ashwini Chaudhary, Commented Jan 22, 2014 at 16:43

Aaron Digulla · Accepted Answer · 2014-01-22 16:46:28Z

2

The simple solution:

Read the whole text into a variable as a string.
Use a multi-line regexp to match what you want to replace
Use output = pattern.sub('replacement', fileContent)

The complex solution:

Read the file line by line
Print any line which doesn't match the start of the pattern
If you find a match for the start, stop printing until you see the end pattern.
If you saw the end pattern, print the replacement

answered Jan 22, 2014 at 16:46

Aaron Digulla

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Martijn Pieters · Accepted Answer · 2014-01-22 16:49:32Z

1

Use pattern.sub('replacement text', text_in_file) to replace matches.

You can use back references in the replacement pattern as needed. It doesn't matter if the string is shorter or longer; the method returns a new string value with the replacements made. If the text came from a file, you'll need to write back the text to that file to replace the contents.

You could use the fileinput module if you need to make the replacement in-place; the module takes care of moving the original file aside and write a new file in it's place.

edited Jan 22, 2014 at 16:49

answered Jan 22, 2014 at 16:44

Martijn Pieters

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