Pythonic way to check if a file exists

Question

Which is the preferred way to check if a file exists and if not create it

User · Accepted Answer

To check if a path is an existing file   os path isfile path      Return True if path is an existing   regular file  This follows symbolic   links  so both islink   and   isfile   can be true for the same   path

User · Answer

This was the best way for me  You can retrieve all existing files  be it symbolic links or normal    os path lexists path   Return True if path refers to an existing path  Returns True for broken symbolic links  Equivalent to exists   on platforms lacking os lstat     New in version 2 4

User · Answer

Instead of os path isfile  suggested by others  I suggest using os path exists  which checks for anything with that name  not just whether it is a regular file   Thus   if not os path exists filename       file filename   w   close     Alternatively   file filename   w    close     The latter will create the file if it exists  but not otherwise  It will  however  fail if the file exists  but you don t have permission to write to it  That s why I prefer the first solution

User · Answer

If  when the file doesn t exist  you want to create it as empty  the simplest approach is  with open thepath   a    pass    in Python 2 6 or better  in 2 5  this requires an  import from the future  at the top of your module    If  on the other hand  you want to leave the file alone if it exists  but put specific non-empty contents there otherwise  then more complicated approaches based on if os path isfile thepath   else statement blocks are probably more suitable

User · Answer

It seems to me that all other answers here  so far  fail to address the race-condition that occurs with their proposed solutions   Any code where you first check for the files existence  and then  a few lines later in your program  you create it  runs the risk of the file being created while you weren t looking and causing you problems  or you causing the owner of  that other file  problems    If you want to avoid this sort of thing  I would suggest something like the following  untested    import os  def open if not exists filename       try          fd   os open filename  os O CREAT   os O EXCL   os O WRONLY      except OSError  e          if e errno    17              print e             return None         else              raise     else          return os fdopen fd   w     This should open your file for writing if it doesn t exist already  and return a file-object  If it does exists  it will print  Ooops  and return None  untested  and based solely on reading the python documentation  so might not be 100  correct

[python] Pythonic way to check if a file exists?

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