Implement touch using Python

Question

touch is a Unix utility that sets the modification and access times of files to the current time of day   If the file doesn t exist  it is created with default permissions   How would you implement it as a Python function  Try to be cross platform and complete    Current Google results for  python touch file  are not that great  but point to os utime

User · Answer

This tries to be a little more race-free than the other solutions. (The with keyword is new in Python 2.5.)

import os
def touch(fname, times=None):
    with open(fname, 'a'):
        os.utime(fname, times)

Roughly equivalent to this.

import os
def touch(fname, times=None):
    fhandle = open(fname, 'a')
    try:
        os.utime(fname, times)
    finally:
        fhandle.close()

Now, to really make it race-free, you need to use futimes and change the timestamp of the open filehandle, instead of opening the file and then changing the timestamp on the filename (which may have been renamed). Unfortunately, Python doesn't seem to provide a way to call futimes without going through ctypes or similar...

EDIT

As noted by Nate Parsons, Python 3.3 will add specifying a file descriptor (when os.supports_fd) to functions such as os.utime, which will use the futimes syscall instead of the utimes syscall under the hood. In other words:

import os
def touch(fname, mode=0o666, dir_fd=None, **kwargs):
    flags = os.O_CREAT | os.O_APPEND
    with os.fdopen(os.open(fname, flags=flags, mode=mode, dir_fd=dir_fd)) as f:
        os.utime(f.fileno() if os.utime in os.supports_fd else fname,
            dir_fd=None if os.supports_fd else dir_fd, **kwargs)

User · Answer

write text   from pathlib Path can be used    gt  gt  gt  from pathlib import Path  gt  gt  gt  Path  aa txt   write text     0

User · Answer

open file name   a   close     did not work for me in Python 2 7 on Windows    os utime file name  None   worked just fine   Also  I had a need to recursively touch all files in a directory with a date older than some date   I created hte following based on ephemient s very helpful response     def touch file name         Update the modified timestamp of a file to now      if not os path exists file name           return     try          os utime file name  None      except Exception          open file name   a   close    def midas touch root path  older than dt now    pattern       recursive False               midas touch updates the modified timestamp of a file or files in a                  directory  folder       Arguements          root path  str   file name or folder name of file-like object to touch         older than  datetime   only touch files with datetime older than this                     datetime         pattern  str   filter files with this pattern  ignored if root path is                 a single file          recursive  boolean   search sub-diretories  ignored if root path is a                    single file                if root path NOT exist  exit     if not os path exists root path           return       if root path DOES exist  continue      else            if root path is a directory  touch all files in root path         if os path isdir root path                 get a directory list  list of files in directory              dir list find files root path  pattern       recursive False                loop through list of files             for f in dir list                    if the file modified date is older thatn older than  touch the file                 if dt fromtimestamp os path getmtime f    lt  older than                      touch f                      print  Touched    f           if root path is a file  touch the file         else                if the file modified date is older thatn older than  touch the file             if dt fromtimestamp os path getmtime f    lt  older than                  touch root path

User · Answer

Complex  possibly buggy    def utime fname  atime None  mtime None      if type atime  is tuple          atime  mtime   atime      if atime is None or mtime is None          statinfo   os stat fname          if atime is None              atime   statinfo st atime         if mtime is None              mtime   statinfo st mtime      os utime fname   atime  mtime     def touch fname  atime None  mtime None       if type atime  is tuple          atime  mtime   atime      open fname   a   close       utime fname  atime  mtime    This tries to also allow setting the access or modification time  like GNU touch

User · Answer

It might seem logical to create a string with the desired variables  and pass it to os system   touch    touch     dir         fileName os system touch    This is inadequate in a number of ways  e g  it doesn t handle whitespace   so don t do it     A more robust method is to use subprocess    subprocess call   touch   os path join dirname  fileName     While this is much better than using a subshell  with os system   it is still only suitable for quick-and-dirty scripts  use the accepted answer for cross-platform programs

User · Answer

Looks like this is new as of Python 3 4 - pathlib   from pathlib import Path  Path  path to file txt   touch     This will create a file txt at the path   --     Path touch mode 0o777  exist ok True       Create a file at this given path  If mode is given  it is combined with the process    umask value to determine the file mode and access flags  If the file already exists  the function succeeds if exist ok is true  and its modification time is updated to the current time   otherwise FileExistsError is raised

User · Answer

Here s some code that uses ctypes  only tested on Linux    from ctypes import   libc   CDLL  libc so 6       struct timespec                 time t tv sec            seconds                  long   tv nsec           nanoseconds                   int futimens int fd  const struct timespec times 2     class c timespec Structure        fields       tv sec   c long     tv nsec   c long    class c utimbuf Structure        fields       atime   c timespec     mtime   c timespec    utimens   CFUNCTYPE c int  c char p  POINTER c utimbuf   futimens   CFUNCTYPE c int  c char p  POINTER c utimbuf       from  usr include i386-linux-gnu bits stat h UTIME NOW      1l  lt  lt  30  - 1l  UTIME OMIT     1l  lt  lt  30  - 2l  now    c timespec 0 UTIME NOW  omit   c timespec 0 UTIME OMIT     wrappers def update atime fileno           assert isinstance fileno  int           libc futimens fileno  byref c utimbuf now  omit    def update mtime fileno           assert isinstance fileno  int           libc futimens fileno  byref c utimbuf omit  now       usage example      f   open   tmp test     update mtime f fileno

User · Answer

For a more low-level solution one can use os close os open  quot file txt quot   os O CREAT

User · Answer

This answer is compatible with all versions since Python-2 5 when keyword with has been released   1  Create file if does not exist   Set current time  exactly same as command touch   import os  fname    directory filename txt  with open fname   a          Create file if does not exist     os utime fname  None     Set access modified times to now                              May raise OSError if file does not exist   A more robust version   import os  with open fname   a      try                        Whatever if file was already existing     os utime fname  None       gt  Set current time anyway   except OSError      pass    File deleted between open   and os utime   calls   2  Just create the file if does not exist  does not update time    with open fname   a       Create file if does not exist     pass   3  Just update file access modified times  does not create file if not existing   import os  try      os utime fname  None     Set access modified times to now except OSError      pass    File does not exist  or no permission    Using os path exists   does not simplify the code   from   future   import  absolute import  division  print function  import os  if os path exists fname     try      os utime fname  None     Set access modified times to now   except OSError      pass    File deleted between exists   and utime   calls              or no permission    Bonus  Update time of all files in a directory  from   future   import  absolute import  division  print function  import os  number of files   0      Current directory which is  walked through            Directories in root              Files in root       Working directory                                      for root     filenames in os walk         for fname in filenames      pathname   os path join root  fname      try        os utime pathname  None     Set access modified times to now       number of files    1     except OSError as why        print  Cannot change time of  r because  r   pathname  why   print  Changed time of  i files   number of files

User · Answer

If you don t mind the try-except then     def touch dir folder path       try          os mkdir folder path      except FileExistsError          pass   One thing to note though  if a file exists with the same name then it won t work and will fail silently

User · Answer

with open file name  a   as f       pass

User · Answer

Why don t you try  newfile py     usr bin env python import sys inputfile   sys argv 1   with open inputfile   w   as file      pass      python newfile py foobar txt   or     use subprocess    import subprocess subprocess call   touch    barfoo txt

User · Answer

def touch fname       if os path exists fname           os utime fname  None      else          open fname   a   close

User · Answer

Simplistic   def touch fname       open fname   a   close       os utime fname  None     The open ensures there is a file there the utime ensures that the timestamps are updated   Theoretically  it s possible someone will delete the file after the open  causing utime to raise an exception  But arguably that s OK  since something bad did happen

User · Answer

Why not try this    import os  def touch fname       try          os utime fname  None      except OSError          open fname   a   close     I believe this eliminates any race condition that matters   If the file does not exist then an exception will be thrown   The only possible race condition here is if the file is created before open   is called but after os utime     But this does not matter because in this case the modification time will be as expected since it must have happened during the call to touch

User · Answer

The following is sufficient   import os def func filename       if os path exists filename           os utime filename      else          with open filename  a   as f              pass   If you want to set a specific time for touch  use os utime as follows   os utime filename  atime mtime     Here  atime and mtime both should be int float and should be equal to epoch time in seconds to the time which you want to set

[python] Implement touch using Python?

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