How to search and replace text in a file

Question

How do I search and replace text in a file using Python 3   Here is my code   import os import sys import fileinput  print   Text to search for    textToSearch   input    gt       print   Text to replace it with    textToReplace   input    gt       print   File to perform Search-Replace on    fileToSearch    input    gt       fileToSearch    D  dummy1 txt   tempFile   open  fileToSearch   r      for line in fileinput input  fileToSearch        if textToSearch in line           print  Match Found       else          print  Match Not Found         tempFile write  line replace  textToSearch  textToReplace     tempFile close     input    n n Press Enter to exit         Input file   hi this is abcd hi this is abcd This is dummy text file  This is how search and replace works abcd   When I search and replace  ram  by  abcd  in above input file  it works as a charm  But when I do it vice-versa i e  replacing  abcd  by  ram   some junk characters are left at the end   Replacing  abcd  by  ram   hi this is ram hi this is ram This is dummy text file  This is how search and replace works rambcd

User · Answer

As Jack Aidley had posted and  J F  Sebastian pointed out  this code will not work      Read in the file filedata   None with file   open  file txt    r       filedata   file read      Replace the target string filedata replace  ram    abcd      Write the file out again with file   open  file txt    w       file write filedata     But this code WILL work  I ve tested it    f   open filein  r   filedata   f read   f close    newdata   filedata replace  old data   new data    f   open fileout  w   f write newdata  f close     Using this method  filein and fileout can be the same file  because Python 3 3 will overwrite the file upon opening for write

User · Answer

You can do the replacement like this  f1   open  file1 txt    r   f2   open  file2 txt    w   for line in f1      f2 write line replace  old text    new text    f1 close   f2 close

User · Answer

With a single with block  you can search and replace your text   with open  file txt   r    as f      filedata   f read       filedata   filedata replace  abc   xyz       f truncate 0      f write filedata

User · Answer

def findReplace find  replace        import os       src   os path join os getcwd    os pardir        for path  dirs  files in os walk os path abspath src             for name in files                if name endswith   py                      filepath   os path join path  name                   with open filepath  as f                        s   f read                    s   s replace find  replace                    with open filepath   w   as f                       f write s

User · Answer

As pointed out by michaelb958  you cannot replace in place with data of a different length because this will put the rest of the sections out of place  I disagree with the other posters suggesting you read from one file and write to another  Instead  I would read the file into memory  fix the data up  and then write it out to the same file in a separate step     Read in the file with open  file txt    r   as file     filedata   file read      Replace the target string filedata   filedata replace  ram    abcd      Write the file out again with open  file txt    w   as file    file write filedata    Unless you ve got a massive file to work with which is too big to load into memory in one go  or you are concerned about potential data loss if the process is interrupted during the second step in which you write data to the file

User · Answer

My variant  one word at a time on the entire file   I read it into memory   def replace word infile old word new word       if not os path isfile infile           print   Error on replace word  not a regular file    infile          sys exit 1       f1 open infile  r   read       f2 open infile  w       m f1 replace old word new word      f2 write m

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I got the same issue  The problem is that when you load a  txt in a variable you use it like an array of string while it s an array of character  swapString      with open filepath  as f       s   f read   for each in s      swapString append str each  replace  this   that    s   swapString print s

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Late answer  but this is what I use to find and replace inside a text file  with open  quot test txt quot   as r    text   r read   replace  quot THIS quot    quot THAT quot   with open  quot test txt quot    quot w quot   as w    w write text   DEMO

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pip install python-util  from pyutil import filereplace  filereplace  quot somefile txt quot   quot abcd quot   quot ram quot    Will replace all occurences of  quot abcd quot  with  quot ram quot   The function also supports regex by specifying regex True from pyutil import filereplace  filereplace  quot somefile txt quot   quot   w  quot   quot ram quot  regex True   Disclaimer  I m the author  https   github com MisterL2 python-util

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fileinput already supports inplace editing  It redirects stdout to the file in this case      usr bin env python3 import fileinput  with fileinput FileInput filename  inplace True  backup   bak   as file      for line in file          print line replace text to search  replacement text   end

User · Answer

Like so   def find and replace file  word  replacement     with open file   r    as f      text   f read       f write text replace word  replacement

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I have worked this out as an exercise of a course  open file  find and replace string and write to a new file  class Letter       def   init   self            with open  quot   Input Names invited names txt quot    quot r quot   as file                read the list of names             list names    line rstrip   for line in file              with open  quot   Input Letters starting letter docx quot    quot r quot   as f                    read letter                 file source   f read               for name in list names                  with open f quot   Output ReadyToSend LetterTo name  docx quot    quot w quot   as f                        replace  name  with name of the list in the file                     replace string   file source replace   name    name                        write to a new file                     f write replace string    brief   Letter

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def word replace filename old new       c 0     with open filename  r   encoding   utf-8   as f          a f read           b a split           for i in range 0 len b                if b i   old                  c c 1         old old center len old  2          new new center len new  2          d a replace old new c          f truncate 0          f seek 0          f write d      print  All words have been replaced

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I have done this      usr bin env python3  import fileinput import os  Dir   input   Source directory     os chdir Dir   Filelist   os listdir   print  File list    Filelist   NomeFile   input   Insert file name      CarOr   input   Text to search      CarNew   input   New text      with fileinput FileInput NomeFile  inplace True  backup   bak   as file      for line in file          print line replace CarOr  CarNew   end      file close

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I modified Jayram Singh s post slightly in order to replace every instance of a     character to a number which I wanted to increment with each instance   Thought it might be helpful to someone who wanted to modify a character that occurred more than once per line and wanted to iterate   Hope that helps someone   PS- I m very new at coding so apologies if my post is inappropriate in any way  but this worked for me   f1   open  file1 txt    r   f2   open  file2 txt    w   n   1      if word     replace w   n   amp  increment n  else append same word to        file2  for line in f1      for word in line          if word                     f2 write word replace      f   n                  n    1         else              f2 write word  f1 close   f2 close

User · Answer

Besides the answers already mentioned  here is an explanation of why you have some random characters at the end  You are opening the file in r  mode  not w mode  The key difference is that w mode clears the contents of the file as soon as you open it  whereas r  doesn t  This means that if your file content is  quot 123456789 quot  and you write  quot www quot  to it  you get  quot www456789 quot   It overwrites the characters with the new input  but leaves any remaining input untouched  You can clear a section of the file contents by using truncate  lt startPosition gt    but you are probably best off saving the updated file content to a string first  then doing truncate 0  and writing it all at once  Or you can use my library  D

User · Answer

Your problem stems from reading from and writing to the same file  Rather than opening fileToSearch for writing  open an actual temporary file and then after you re done and have closed tempFile  use os rename to move the new file over fileToSearch

User · Answer

You can also use pathlib   from pathlib2 import Path path   Path file to search  text   path read text   text   text replace text to search  replacement text  path write text text

[python] How to search and replace text in a file?

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