[python] Implement touch using Python?

^{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)  # => 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)