open in Python does not create a file if it doesn t exist

Question

What is the best way to open a file as read write if it exists  or if it does not  then create it and open it as read write  From what I read  file   open  myfile dat    rw   should do this  right   It is not working for me  Python 2 6 2  and I m wondering if it is a version problem  or not supposed to work like that or what   The bottom line is  I just need a solution for the problem  I am curious about the other stuff  but all I need is a nice way to do the opening part   The enclosing directory was writeable by user and group  not other  I m on a Linux system    so permissions 775 in other words   and the exact error was      IOError  no such file or directory

User · Answer

What do you want to do with file  Only writing to it or both read and write    w    a  will allow write and will create the file if it doesn t exist   If you need to read from a file  the file has to be exist before open it  You can test its existence before opening it or use a try except

User · Answer

w  write mode r  read mode a  append mode  w   create file if it doesn t exist and open it in write mode r   open for reading and writing  Does not create file  a   create file if it doesn t exist and open it in append mode       example   file name    my file txt  f   open file name   w       open file in write mode f write  python rules   f close     I hope this helps   FYI am using python version 3 6 2

User · Answer

If you want to open it to read and write  I m assuming you don t want to truncate it as you open it and you want to be able to read the file right after opening it  So this is the solution I m using   file   open  myfile dat    a    file seek 0  0

User · Answer

import os  platform os chdir  c   Users  MS  Desktop    try       file   open  Learn Python txt   a       print  this file is exist   except      print  this file is not exist   file write   n  Hello Ashok    fhead   open  Learn Python txt    for line in fhead       words   line split   print words

User · Answer

Change  rw  to  w    Or use  a   for appending  not erasing existing content

User · Answer

Put w  for writing the file  truncating if it exist  r  to read the file  creating one if it don t exist but not writing  and returning null  or a  for creating a new file or appending to a existing one

User · Answer

open  myfile dat    a   works for me  just fine   in py3k your code raises ValueError    gt  gt  gt  open  myfile dat    rw   Traceback  most recent call last     File   lt pyshell 34 gt    line 1  in  lt module gt      open  myfile dat    rw   ValueError  must have exactly one of read write append mode   in python-2 6 it raises IOError

User · Answer

My answer   file path    myfile dat  try      fp   open file path  except IOError        If not exists  create the file     fp   open file path   w

User · Answer

Good practice is to use the following   import os  writepath    some path to file txt   mode    a  if os path exists writepath  else  w  with open writepath  mode  as f      f write  Hello  world  n

User · Answer

I think it s r   not rw  I m just a starter  and that s what I ve seen in the documentation

User · Answer

You should use open with the w  mode   file   open  myfile dat    w

User · Answer

The advantage of the following approach is that the file is properly closed at the block s end  even if an exception is raised on the way  It s equivalent to try-finally  but much shorter   with open  file dat   a    as f      f write                   a  Opens a file for both appending and reading  The file pointer is   at the end of the file if the file exists  The file opens in the   append mode  If the file does not exist  it creates a new file for   reading and writing  -Python file modes   seek   method sets the file s current position   f seek pos     0 1 2    pos    position of the r w pointer       optionally       one of - gt    0    absolute position   1    relative position to current   2    relative position from end      Only  rwab   characters are allowed  there must be exactly one of  rwa  - see Stack nbsp Overflow question Python file modes detail

User · Answer

For Python 3   I will do  import os  os makedirs  path to the directory   exist ok True   with open  path to the directory filename    w   as f      f write       So  the problem is with open cannot create a file before the target directory exists  We need to create it and then w mode is enough in this case

User · Answer

gt  gt  gt  import os  gt  gt  gt  if os path exists  myfile dat            f   file  myfile dat    r        else          f   file  myfile dat    w     r  means read write

User · Answer

Since python 3 4 you should use pathlib to  touch  files  It is a much more elegant solution than the proposed ones in this thread   from pathlib import Path  filename   Path  myfile txt   filename touch exist ok True     will create file  if it exists will do nothing file   open filename    Same thing with directories   filename mkdir parents True  exist ok True

User · Answer

So You want to write data to a file  but only if it doesn   t already exist    This problem is easily solved by using the little-known x mode to open   instead of the usual w mode  For example     gt  gt  gt  with open  somefile    wt   as f           f write  Hello n        gt  gt  gt  with open  somefile    xt   as f          f write  Hello n        Traceback  most recent call last    File   lt stdin gt    line 1  in  lt module gt  FileExistsError   Errno 17  File exists   somefile     gt  gt  gt    If the file is binary mode  use mode xb instead of xt

User · Answer

Use   import os  f loc   r C  Users Russell Desktop myfile dat     Create the file if it does not exist if not os path exists f loc       open f loc   w   close      Open the file for appending and reading with open f loc   a    as f       Do stuff   Note  Files have to be closed after you open them  and the with context manager is a nice way of letting Python take care of this for you

[python] open() in Python does not create a file if it doesn't exist

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