How to Delete Subsequent Line After A Line With Specific Keyword in Python

Question

After finding a specific line with keyword "banana", I would like to delete the subsequent line, in this case, "berry".

Sample.txt

orange
apple
banana
berry
melon

My script, however, deletes "banana" not "berry"....Why?

import fileinput

filename = r"C:\sample.txt"
for linenum,line in enumerate(fileinput.FileInput(filename, inplace=1)):
    if "banana" in line:
        counter = linenum + 1
        if linenum == counter:
            line.strip()
    else:
        print line,

first of all, this script never deletes anything, in fact, what i can see is that it prints any line in the file, unless 'banana' is in the line, in which case it increases a counter and then strips whitespace from the end of the current line.... i suggest you read up on your python skills, because this is not doing anything. — Inbar Rose, Jan 14 '13 at 08:43
comment made by @Inbar Rose is valid. The flaw in your code is that you're not deleting anything. In fact you're actually rewriting the whole file. You're re-printing all lines except for the one that has "banana" in it. And inplace=1 is allowing you to do that. — tigeronk2, Jan 14 '13 at 10:13
@InbarRose In this case, it is you who should read up on your python skills. Try the answer (and comments) [here](http://stackoverflow.com/a/290494/674039) for example. — wim, Jan 15 '13 at 15:04

Jon Clements · Accepted Answer · 2013-01-14T09:11:01.120

3

Do it like this:

import fileinput

fin = fileinput.input('/home/jon/text.txt', inplace=1)
for line in fin:
    print line,
    if line.strip() == 'banana':
        next(fin, None) # as suggested by @thg435 doesn't hurt to use default to avoid StopIteration (as next iteration will just be a no-op anyway)

This takes advantage of iterating the fin object so it doesn't see the next row - meaning you don't have to worry about setting/unsetting flags... (which can lead to errors)

edited Jan 14 '13 at 09:11

answered Jan 14 '13 at 08:54

Jon Clements

138,671
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1

I'd use `next(fin, None)`, just in case. – georg Jan 14 '13 at 09:07

cleg · Answer 2 · 2013-01-14T08:56:24.390

2

Something like this:

flag = False
with open("C:\sample.txt") as in_f:
    for line in in_f:
        if flag: # previous line have "banana", so skip this line
            flag = False
            continue
        if "banana" in line: # set flag to skip line
            flag = True
        print line

edited Jan 14 '13 at 08:56

answered Jan 14 '13 at 08:47

cleg

4,862
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Change the __pring__ to `print` – Matthias Jan 14 '13 at 08:53
@cleg: thanks for the advice. I never knew you could use the "flag" like that. Good learning experience. Thanks again. – fairyberry Jan 14 '13 at 08:59
@Inbar: I see. Good observation. Though, as long as I can print out all the lines except the one I want to delete, then it would help me to rewrite the file except the one. Thanks. – fairyberry Jan 14 '13 at 09:11
@user1027101 you're welcome. it's common practice actually. BTW, it's very-very simple example of finite state machine — mechanism, used for parsers and comliers :) – cleg Jan 14 '13 at 09:11
@user1027101 also, often use "skipping" instead of "deleting" — is also a solution – cleg Jan 14 '13 at 09:12

score 1 · Answer 3 · answered Jan 14 '13 at 08:54

1

Please try this

filename = r"sample.txt"
counter = -1
for linenum,line in enumerate(fileinput.FileInput(filename, inplace=1)):
    if "banana" in line:
        counter = linenum + 1
    if linenum == counter:
        line.strip()
    else:
        print line,

answered Jan 14 '13 at 08:54

fwu

359
2
10

it works!! and I am wondering why you put like "counter = -1"? – fairyberry Jan 14 '13 at 09:27

How to Delete Subsequent Line After A Line With Specific Keyword in Python

3 Answers3