ActiveState Code

Recipe 576804: Find the oldest (or yougest) of a list of files

Sometimes you need to perform an operation on the oldest of a set of files. Using get_oldest_file you could implement an age-based priority queue that processes files from oldest to newest. The list of files you pass in may be from a glob of a single directory or some more elaborate search routine.

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import os, glob, time, operator

def get_oldest_file(files, _invert=False):
    """ Find and return the oldest file of input file names.
    Only one wins tie. Values based on time distance from present.
    Use of `_invert` inverts logic to make this a youngest routine,
    to be used more clearly via `get_youngest_file`.
    """
    gt = operator.lt if _invert else operator.gt
    # Check for empty list.
    if not files:
        return None
    # Raw epoch distance.
    now = time.time()
    # Select first as arbitrary sentinel file, storing name and age.
    oldest = files[0], now - os.path.getctime(files[0])
    # Iterate over all remaining files.
    for f in files[1:]:
        age = now - os.path.getctime(f)
        if gt(age, oldest[1]):
            # Set new oldest.
            oldest = f, age
    # Return just the name of oldest file.
    return oldest[0]

def get_youngest_file(files):
    return get_oldest_file(files, _invert=True)

# Example.
files = glob.glob('*.py')
print 'oldest:', get_oldest_file(files)
print 'youngest:', get_youngest_file(files)

Discussion

Of course this is simpler in a shell with something like: ls -t *.py |head -1 but often shelling out is not an option. And this recipe demonstrates some useful time math.

Comments

  1. 1. At 6:31 p.m. on 10 jun 2009, Mike Kazantsev said:

    It would be much simplier and faster to hand the task down to built-in sorted function:

    import os

files = sorted(os.listdir(path), key=os.path.getctime)

oldest = files[0]
newest = files[-1]
  2. 2. At 10:50 p.m. on 10 jun 2009, Micah Elliott (the author) said:

    Wow, that's quite an improvement. Thanks Mike!

  3. 3. At 8:46 a.m. on 12 jun 2009, Matteo Dell'Amico said:

    You can actually avoid sorting the whole list.

    min(os.listdir(path), key=os.path.getctime)
max(os.listdir(path), key=os.path.getctime)

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