Replace and overwrite instead of appending

Question

I have the following code   import re  open the xml file for reading  file   open  path test xml   r     convert to string  data   file read   file write re sub r  lt string gt ABC lt  string gt   s   lt string gt      lt  string gt   r  lt xyz gt ABC lt  xyz gt  1 lt xyz gt  2 lt  xyz gt   data   file close     where I d like to replace the old content that s in the file with the new content  However  when I execute my code  the file  test xml  is appended  i e  I have the old content follwed by the new  replaced  content  What can I do in order to delete the old stuff and only keep the new

User · Answer

import os must import this library if os path exists  TwitterDB csv            os remove  TwitterDB csv    this deletes the file else          print  The file does not exist   add this to prevent errors   I had a similar problem  and instead of overwriting my existing file using the different  modes   I just deleted the file before using it again  so that it would be as if I was appending to a new file on each run of my code

User · Answer

Using python3 pathlib library  import re from pathlib import Path import shutil  shutil copy2  quot  tmp test xml quot    quot  tmp test xml bak quot     create backup filepath   Path  quot  tmp test xml quot   content   filepath read text   filepath write text re sub r quot  lt string gt ABC lt  string gt   s   lt string gt      lt  string gt  quot  r quot  lt xyz gt ABC lt  xyz gt  1 lt xyz gt  2 lt  xyz gt  quot   content    Similar method using different approach to backups  from pathlib import Path  filepath   Path  quot  tmp test xml quot   filepath rename filepath with suffix   bak      different approach to backups content   filepath read text   filepath write text re sub r quot  lt string gt ABC lt  string gt   s   lt string gt      lt  string gt  quot  r quot  lt xyz gt ABC lt  xyz gt  1 lt xyz gt  2 lt  xyz gt  quot   content

User · Answer

Using truncate    the solution could be  import re  open the xml file for reading  with open  path test xml   r    as f       convert to string      data   f read       f seek 0      f write re sub r  lt string gt ABC lt  string gt   s   lt string gt      lt  string gt   r  lt xyz gt ABC lt  xyz gt  1 lt xyz gt  2 lt  xyz gt   data       f truncate

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See from How to Replace String in File works in a simple way and is an answer that works with replace  fin   open  data txt    rt   fout   open  out txt    wt    for line in fin      fout write line replace  pyton    python     fin close   fout close

User · Answer

file  path test xml   with open file   w   as filetowrite      filetowrite write  new content     Open the file in  w  mode  you will be able to replace its current text save the file with new contents

User · Answer

You need seek to the beginning of the file before writing and then use file truncate   if you want to do inplace replace   import re  myfile    path test xml   with open myfile   r    as f      data   f read       f seek 0      f write re sub r  lt string gt ABC lt  string gt   s   lt string gt      lt  string gt    r  lt xyz gt ABC lt  xyz gt  1 lt xyz gt  2 lt  xyz gt    data       f truncate     The other way is to read the file then open it again with open myfile   w     with open myfile   r   as f      data   f read    with open myfile   w   as f      f write re sub r  lt string gt ABC lt  string gt   s   lt string gt      lt  string gt    r  lt xyz gt ABC lt  xyz gt  1 lt xyz gt  2 lt  xyz gt    data     Neither truncate nor open       w   will change the inode number of the file  I tested twice  once with Ubuntu 12 04 NFS and once with ext4    By the way  this is not really related to Python  The interpreter calls the corresponding low level API  The method truncate   works the same in the C programming language  See http   man7 org linux man-pages man2 truncate 2 html

[python] Replace and overwrite instead of appending

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