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.)

Here's the source for GNU touch.

Answer 1

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

Answer 2

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.

Answer 3

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.

Answer 4

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 file(fname, 'a'):
        os.utime(fname, times)

Roughly equivalent to this.

import os
def touch(fname, times = None):
    fhandle = file(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...