I have got the following requirement:
In a file that has many lines, i need to search for a particular line that has the word DTP. The line may be like this in the file:
src dst DTP 0 - 65000
If the line with the word "DTP" is found, then that line has to be removed from the file.
How to do this?
Also in some cases I need to replace that word with another word and then write that line back to the file.
I have looked at some of the file programs that use readlines, read etc, but haven't found anything that solves my issues.
any help would be very much valuable for me.


6 Years
Discussion Span
Last Post by Beat_Slayer

Here is one way to accomplish this. I don't know which version of Python you are using. If you have a newer version you may want to use a with statement to simplify this experimental code a little ...

# read a file line by line and write out a new file
# that excludes any line with a given search string

# raw data for the test file
test_data = """\
src dst DTQ 0 - 65000
src dst DTM 0 - 65000
src dst DTA 0 - 65000
src dst DTP 0 - 65000
src dst DTF 0 - 65000"""

# write the test file
fname_test = "atest_raw.txt"
fout = open(fname_test, "w")

# create a filename for the changed file
fname_out = "atest_out.txt"

# c make the file handles for the in and out files
fh_in = open(fname_test, "r")
fh_out = open(fname_out, "w")

# loop through the test file line by line
# and write only the lines back out that do
# not contain the search string
search = "DTP"
for line in fh_in:
    if search not in line:

# close the file handles

# now you can take an editor to look at file "atest_out.txt"
# and see if the line with the search string in it is missing

This rather simple approach has a caveat, if "DTP" appears in the line inside another word like "ADTPW" this would also remove that line.

Should your file contain this possibility, you have to split each line into a list of words, or use module re. Also, if you know that "DTP" is always surrounded by spaces, you can change the search word to include the spaces " DTP "

Edited by vegaseat: caveat


Something like:

f_in = open('input.txt', 'r')
f_out = open('output.txt', 'w')

for line in f_in:
    if line.find('DTP') == 0:


f_in = open('input.txt', 'r')
f_out = open('output.txt', 'w')

for line in f_in:
    line.replace('DTP', 'NEW_WORD')

Sorry for the lazyness, but I'm not at home.


A simple test of the following code posted above shows that it will only find 'DTP' if it is at the beginning of the line. It should read as indicated.

f_in = ["xyz", "abcDTPxyz", "DTPabc"]
for line in f_in:

    ## the if statement should read
    ## if line.find('DTP') > -1: as line.find() returns the position found
    if line.find('DTP') == 0:
        print "DTP found in", line

DTP found in DTPabc

Edited by woooee: n/a


The intention was to give negative condition on the lines with 'DTP', and not to give positive.

Anyway a litle more refreshed.

f_in = open('input.txt', 'r')
f_out = open('output.txt', 'w')

for line in f_in:
    if 'DTP' not in line:
        f_out.write(line.replace('DTP', 'NEW_WORD'))


Edited by Beat_Slayer: n/a

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