How to find and replace multiple lines in text file?
file, python, replace, string
Solution
If the file is large, you want to `read` and `write` one line at a time, so the whole thing isn't loaded into memory at once.
# create a dict of find keys and replace values
findlines = open('find.txt').read().split('\n')
replacelines = open('replace.txt').read().split('\n')
find_replace = dict(zip(findlines, replacelines))
with open('data.txt') as data:
with open('new_data.txt', 'w') as new_data:
for line in data:
for key in find_replace:
if key in line:
line = line.replace(key, find_replace[key])
new_data.write(line)
Edit: I changed the code to `read().split('\n')` instead of `readliens()` so `\n` isn't included in the find and replace strings
Problem
I am running Python 2.7. I have three text files: `data.txt`, `find.txt`, and `replace.txt`. Now, `find.txt` contains several lines that I want to search for in `data.txt` and replace that section with the content in `replace.txt`. Here is a simple example: data.txt ``` pumpkin apple banana cherry himalaya skeleton apple banana cherry watermelon fruit ``` find.txt ``` apple banana cherry ``` replace.txt ``` 1 2 3 ``` So, in the above example, I want to search for all occurences of `apple`, `banana`, and `cherry` in the data and replace those lines with `1,2,3`. I am having some trouble with the right approach to this as my `data.txt` is about 1MB so I want to be as efficient as possible. One dumb way is to concatenate everything into one long string and use `replace`, and then output to a new text file so all the line breaks will be restored. ``` import re data = open("data.txt", 'r') find = open("find.txt", 'r') replace = open("replace.txt", 'r') data_str = "" find_str = "" replace_str = "" for line in data: # concatenate it into one long string data_str += line for line in find: # concatenate it into one long string find_str += line for line in replace: replace_str += line new_data = data_str.replace(find, replace) new_file = open("new_data.txt", "w") new_file.write(new_data) ``` But this seems so convoluted and inefficient for a large data file like mine. Also, the `replace` function appears to be deprecated so that's not good. Another way is to step through the lines and keep a track of which line you found a match. Something like this: ``` location = 0 LOOP1: for find_line in find: for i, data_line in enumerate(data).startingAtLine(location): if find_line == data_line: location = i # found possibility for idx in range(NUMBER_LINES_IN_FIND): if find_line[idx] != data_line[idx+location] # compare line by line #if the subsequent lines don't match, then go back and search again goto LOOP1 ``` Not fully formed code, I know. I don't even know if it's possible to search through a file from a certain line on or between certain lines but again, I'm just a bit confused in the logic of it all. What is the best way to do this? Thanks!