Create a file if it doesn t exist

Question

I m trying to open a file  and if the file doesn t exist  I need to create it and open it for writing  I have this so far    open file for reading fn   input  Enter file to open     fh   open fn  r     if file does not exist  create it if   fh   fh   open   fh   w     The error message says there s an issue on the line if  fh   Can I use exist like in Perl

User · Answer

If you don t need atomicity you can use os module   import os  if not os path exists   tmp test        os mknod   tmp test     UPDATE   As Cory Klein mentioned  on Mac OS for using os mknod   you need a root permissions  so if you are Mac OS user  you may use open   instead of os mknod    import os  if not os path exists   tmp test        with open   tmp test    w    pass

User · Answer

Well  first of all  in Python there is no   operator  that d be not  But open would not fail silently either - it would throw an exception  And the blocks need to be indented properly - Python uses whitespace to indicate block containment   Thus we get   fn   input  Enter file name     try      file   open fn   r   except IOError      file   open fn   w

User · Answer

Here s a quick two-liner that I use to quickly create a file if it doesn t exists  if not os path exists filename       open filename   w   close

User · Answer

Be warned  each time the file is opened with this method the old data in the file is destroyed regardless of  w   or just  w      import os  with open  file txt    w    as f      f write  file is opened for business

User · Answer

Using input   implies Python 3  recent Python 3 versions have made the IOError exception deprecated  it is now an alias for OSError    So assuming you are using Python 3 3 or later   fn   input  Enter file name     try      file   open fn   r   except FileNotFoundError      file   open fn   w

User · Answer

I think this should work    open file for reading fn   input  Enter file to open     try      fh   open fn  r   except    if file does not exist  create it     fh   open fn  w     Also  you incorrectly wrote fh   open   fh   w   when the file you wanted open was fn

User · Answer

w  write mode r  read mode a  append mode  w   create file if it doesn t exist and open it in  over write mode      it overwrites the file if it already exists  r   open an existing file in read write mode a   create file if it doesn t exist and open it in append mode       example   file name    my file txt  f   open file name   a       open file in append mode f write  python rules   f close     I hope this helps   FYI am using python version 3 6 2

User · Answer

First let me mention that you probably don t want to create a file object that eventually can be opened for reading OR writing  depending on a non-reproducible condition  You need to know which methods can be used  reading or writing  which depends on what you want to do with the fileobject   That said  you can do it as That One Random Scrub proposed  using try      except   Actually that is the proposed way  according to the python motto  It s easier to ask for forgiveness than permission    But you can also easily test for existence   import os   open file for reading fn   raw input  Enter file to open     if os path exists fn       fh   open fn   r   else      fh   open fn   w     Note  use raw input   instead of input    because input   will try to execute the entered text  If you accidently want to test for file  import   you d get a SyntaxError

[python] Create a file if it doesn't exist

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