How to delete a specific line in a file

Question

Let s say I have a text file full of nicknames  How can I delete a specific nickname from this file  using Python

User · Answer

If you use Linux  you can try the following approach  Suppose you have a text file named animal txt                     cat animal txt   dog pig cat  monkey          elephant     Delete the first line    gt  gt  gt  import subprocess  gt  gt  gt  subprocess call   sed   -i      dog   d   animal txt       then            cat animal txt pig cat monkey elephant

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This is a  fork  from  Lother s answer  which I believe that should be considered the right answer     For a file like this     cat file txt  1  october rust 2  november rain 3  december snow   This fork from Lother s solution works fine      usr bin python3 4  with open  file txt   r    as f      new f   f readlines       f seek 0      for line in new f          if  snow  not in line              f write line      f truncate     Improvements     with open  which discard the usage of f close   more clearer if else for evaluating if string is not present in the current line

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here s some other method to remove a some line s  from a file   src file   zzzz txt f   open src file   r   contents   f readlines   f close    contents pop idx    remove the line item from list  by line number  starts from 0  f   open src file   w   contents      join contents  f write contents  f close

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The best and fastest option  rather than storing everything in a list and re-opening the file to write it  is in my opinion to re-write the file elsewhere  with open  quot yourfile txt quot    quot r quot   as file input      with open  quot newfile txt quot    quot w quot   as output           for line in file input              if line strip  quot  n quot       quot nickname to delete quot                   output write line   That s it  In one loop and one only you can do the same thing  It will be much faster

User · Answer

Take the contents of the file  split it by newline into a tuple   Then  access your tuple s line number  join your result tuple  and overwrite to the file

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I liked the fileinput approach as explained in this answer  Deleting a line from a text file  python   Say for example I have a file which has empty lines in it and I want to remove empty lines  here s how I solved it   import fileinput import sys for line number  line in enumerate fileinput input  file1 txt   inplace 1        if len line   gt  1              sys stdout write line       Note  The empty lines in my case had length 1

User · Answer

You can use the re library   Assuming that you are able to load your full txt-file  You then define a list of unwanted nicknames and then substitute them with an empty string        Delete unwanted characters import re    Read  then decode for py2 compat  path to file    data nicknames txt  text   open path to file   rb   read   decode encoding  utf-8      Define unwanted nicknames and substitute them unwanted nickname list     SourDough   text   re sub     join unwanted nickname list       text

User · Answer

I think if you read the file into a list  then do the you can iterate over the list to look for the nickname you want to get rid of  You can do it much efficiently without creating additional files  but you ll have to write the result back to the source file   Here s how I might do this   import  os  csv   and other imports you need nicknames to delete     Nick    Stephen    Mark     I m assuming nicknames csv contains data like   Nick Maria James Chris Mario Stephen Isabella Ahmed Julia Mark       Then load the file into the list    nicknames   None  with open  nicknames csv   as sourceFile       nicknames   sourceFile read   splitlines     Next  iterate over to list to match your inputs to delete   for nick in nicknames to delete       try           if nick in nicknames               nicknames pop nicknames index nick            else               print nick     is not found in the file        except ValueError           pass   Lastly  write the result back to file   with open  nicknames csv    a   as nicknamesFile      nicknamesFile seek 0      nicknamesFile truncate       nicknamesWriter   csv writer nicknamesFile      for name in nicknames          nicknamesWriter writeRow  str name    nicknamesFile close

User · Answer

In general  you can t  you have to write the whole file again  at least from the point of change to the end    In some specific cases you can do better than this -  if all your data elements are the same length and in no specific order  and you know the offset of the one you want to get rid of  you could copy the last item over the one to be deleted and truncate the file before the last item   or you could just overwrite the data chunk with a  this is bad data  skip it  value or keep a  this item has been deleted  flag in your saved data elements such that you can mark it deleted without otherwise modifying the file   This is probably overkill for short documents  anything under 100 KB

User · Answer

Save the file lines in a list  then remove of the list the line you want to delete and write the remain lines to a new file   with open  file name txt    r   as f      lines   f readlines        lines remove  Line you want to delete n       with open  new file txt    w   as new f          for line in lines                      new f write line

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I like this method using fileinput and the  inplace  method   import fileinput for line in fileinput input fname  inplace  1       line   line strip       if not  UnwantedWord  in line          print line    It s a little less wordy than the other answers and is fast enough for

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To delete a specific line of a file by its line number     Replace variables filename and line to delete with the name of your file and the line number you want to delete   filename    foo txt  line to delete   3 initial line   1 file lines       with open filename  as f      content   f readlines     for line in content      file lines initial line    line strip       initial line    1  f   open filename   w   for line number  line content in file lines items        if line number    line to delete          f write     n  format line content    f close   print  Deleted line      format line to delete     Example output   Deleted line  3

User · Answer

Solution to this problem with only a single open   with open  target txt    r    as f      d   f readlines       f seek 0      for i in d          if i     line you want to remove                  f write i      f truncate     This solution opens the file in r w mode   r    and makes use of seek to reset the f-pointer then truncate to remove everything after the last write

User · Answer

Do you want to remove a specific line from file so use this snippet short and simple code you can easily remove any line with sentence or prefix Symbol   with open  quot file name txt quot    quot r quot   as f  lines   f readlines    with open  quot new file txt quot    quot w quot   as new f      for line in lines          if not line startswith  quot write any sentence or symbol to remove line quot                new f write line

User · Answer

The issue with reading lines in first pass and making changes  deleting specific lines  in the second pass is that if you file sizes are huge  you will run out of RAM  Instead  a better approach is to read lines  one by one  and write them into a separate file  eliminating the ones you don t need  I have run this approach with files as big as 12-50 GB  and the RAM usage remains almost constant  Only CPU cycles show processing in progress

User · Answer

First  open the file and get all your lines from the file  Then reopen the file in write mode and write your lines back  except for the line you want to delete   with open  yourfile txt    r   as f      lines   f readlines   with open  yourfile txt    w   as f      for line in lines          if line strip   n       nickname to delete               f write line    You need to strip   n   the newline character in the comparison because if your file doesn t end with a newline character the very last line won t either

User · Answer

Probably  you already got a correct answer  but here is mine  Instead of using a list to collect unfiltered data  what readlines   method does   I use two files  One is for hold a main data  and the second is for filtering the data when you delete a specific string   Here is a code   main file   open  data base txt   read        your main dataBase file filter file   open  filter base txt    w   filter file write main file  filter file close   main file   open  data base txt    w   for line in open  filter base        if  your data to delete  not in line       remove a specific string         main file write line                   put all strings back to your db except deleted     else  pass main file close     Hope you will find this useful

[python] How to delete a specific line in a file?

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