Implement touch using Python?

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.

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)

def touch(fname):
    if os.path.exists(fname):
        os.utime(fname, None)
    else:
        open(fname, 'a').close()

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().