How to delete text in text file using Python based on conditions?

Question

I have a text file from which I want to delete all data up to the point where I see the value 'NODATACODE' . The text in the text file is:

MMMMM ; MMMMM : MMMMMMMMMMN, AAAAAAAAAAA,52, AAAA,CCCCCC, MMMMM ; MMMMM : MMMMMMMMMMN, 
  >AAAAAAAAAAA,200, AAAA,CCCCCC,;MMMMM ; MMMMM : MMMMMMMMMMN, AAAAAAAAAAA,53, 
  >AAAA,CCCCCC,AAAA AAAAA AAAAAAAAAAA AAAAAAAAAAA AAAAAAAAAAA NODATACODE, : Food Meal

Please let me know how I can rewrite the following code in Python to perform this task. I tried the following code but it doesn't work:

with open('Schedule.txt', 'w') as fw:
   for line in lines:
   if line.strip('\n') = 'NODATACODE':
                      fw.write(line)

Error message that I get is below:

     Cell In[1], line 5
     if line.strip('\n') = 'NODATACODE':
        ^
     SyntaxError: cannot assign to function call here. Maybe you meant '==' instead of 
       '='?

Original Output

Desired Output

Thank you in advance.

Line 5 should be !=, but this is a wild guess since your question is not clear enough. In that file are those lines separated by line breaks? Are there more lines after "NODATACODE"? The indentation is wrong. And I think you might need a read handle to get all the lines first, close it and write handle to write the lines you want. — foobar test test test potato
– foobar test test test potato, Commented Dec 25, 2023 at 8:56
@AnalysisNerd, can you make a meaningful example and show the exact matching expected output ? — Timeless
– Timeless, Commented Dec 25, 2023 at 9:00
@Timeless. Just making the required edits to my question. Thank you for your patience. — AnalysisNerd
– AnalysisNerd, Commented Dec 25, 2023 at 9:03

Swifty · Accepted Answer · 2023-12-25 09:34:02Z

0

This should do what you want; note that we test whether the line begins with 'NODATACODE', not is equal to it. And we use a flag so that the next lines will be written to the output file too:

with open('input_file.txt') as f_in:
    with open('output_file.txt', 'w') as f_out:
        write_flag = False
        for line in f_in.readlines():
            if line.startswith('NODATACODE'):
                write_flag = True
            if write_flag:
                f_out.write(line)

If 'NODATACODE' is likely to be inside a line, an approach with regex could be better:

import re

with open('input_file.txt') as f_in:
    with open('output_file.txt', 'w') as f_out:
        data = f_in.read()
        f_out.write(re.sub(r'[\w\W]*NODATACODE', 'NODATACODE', data))

edited Dec 25, 2023 at 9:34

answered Dec 25, 2023 at 9:17

Swifty

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3 Comments

AnalysisNerd Over a year ago

Thank you @swifty! I will try this piece of code promptly. I was just wondering if this 'NOTDATACODE' is in the middle of a line is there a way of deleting all data before it?

Swifty Over a year ago

If NODATACODE is likely to be in the middle of the line, perhaps another approach using a regexp is in order.

AnalysisNerd Over a year ago

Thank you @Swifty. That is a new approach I will try out.

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