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Accept or reject items based on age categorization.

Project Description

Timegaps is a cross-platform command line program. It sorts a set of items into rejected and accepted ones, based on the age of each item and user-given time categorization rules.

Timegaps allows for thinning out a collection of items, whereas the time gaps between accepted items become larger with increasing age of items. This is useful for implementing backup retention policies with the goal to keep backups “logarithmically” distributed in time, e.g. one for each of the last 24 hours, one for each of the last 30 days, one for each of the last 8 weeks, and so on.

Timegaps is built with a focus on reliability. It is backed by a considerable set of unit tests, including direct command line interface tests. Currently, each commit is automatically tested against CPython 2.7/3.3/3.4 on Linux via Travis CI. Releases are tested on Linux as well as on Windows. Simplicity and compliance with the Unix philosophy are the major design goals of timegaps. Version tags follow the concept of semantic versioning.


Timegaps requires Python. Releases are tested on CPython 2.7/3.3/3.4, on Linux as well as on Windows. This is where you can expect it to run properly.


Installation via pip is recommended:

$ pip install timegaps

This downloads the latest timegaps releases from PyPI and installs it. A previously installed version can be upgraded via:

$ pip install --upgrade timegaps

This is how to install the latest development version:

$ pip install git+

Documentation and changelog

  • Docs and resources: the official home of this program is The documentation consists of this README, timegaps --help, and timegaps --extended-help.
  • Changelog.

Hands-on introduction

Consider the following situation: all *.tar.gz files in the current working directory happen to be daily snapshots of something. The task is to accept one snapshot for each of the last 20 days, one for each for the last 8 weeks, and one for each of the last 12 months, and to reject all others. Use timegaps for performing this categorization into rejected and accepted items and print the rejected ones:

$ timegaps days20,weeks8,months12 *.tar.gz | sort

This was a read-only, non-invasive operation. By default, timegaps prints the rejected items to stdout, separated by newline characters (for compatibility with other Unix command line tools). Repeat the operation and count the rejected items:

$ timegaps days20,weeks8,months12 *.tar.gz | wc -l

Given this specific set of rules and set of items, timegaps identified 125 items to be rejected. Move them to the directory notneededanymore (and suppress stdout):

$ mkdir notneededanymore
$ timegaps --move notneededanymore days20,weeks8,months12 *.tar.gz > /dev/null

Count files in the newly created directory for validation purposes (must also be 125):

$ /bin/ls -1 notneededanymore/* | wc -l

Okay, so far the item modification time was determined from the inode via the stat() system call. In a different mode of operation (--time-from- basename), timegaps can read the “modification time” from the basename. The file names of the tarred snapshots in this hands-on session carry meaningful time information, in a certain format (daily-%Y-%m-%d-%H%M%S.tar.gz). Providing this format string, we can instruct timegaps to parse the time from these file names:

$ mv notneededanymore/* .
$ timegaps --time-from-basename daily-%Y-%m-%d-%H%M%S.tar.gz \
    days20,weeks8,months12 *.tar.gz | wc -l

The above can be useful in cases where the actual file modification time is screwed, and the real timing information is only contained in the file name. In another mode of operation (--stdin), timegaps can read newline-separated items from stdin, instead of reading items from the command line:

$ /bin/ls -1 *tar.gz | timegaps --stdin days20,weeks8,months12 | wc -l

Given -0/--nullsep, timegaps can handle NUL character-separated items on stdin. In this mode of operation, timegaps also NUL-separates the items on stdout:

$ find . -name "*tar.gz" -print0 | \
    timegaps -0 --stdin days20,weeks8,months12 | \
    tr '\0' '\n' | wc -l

By default, the reference time for determining the age of items is the time of program invocation. Use -t/--reference-time for changing the reference time from now to an arbitrary date (January 1st, 2020 in this case):

$ timegaps --reference-time 20200101-000000 years10 *.tar.gz | wc -l

With a different reference time and different rules the number of rejected items obviously changed (from 125 to 153). Instead of printing the rejected items, timegaps can invert the output and print the accepted ones:

$ timegaps -a -t 20200101-000000 years10 *.tar.gz

There are more features, such as deleting files, or a mode in which items are treated as simple strings instead of paths. See the help message:

$ timegaps --help
usage: timegaps [-h] [--extended-help] [--version] [-s] [-0] [-a] [-t TIME]
                [--time-from-basename FMT | --time-from-string FMT]
                [-d | -m DIR] [-r] [-v]
                RULES [ITEM [ITEM ...]]

Accept or reject items based on age categorization.

positional arguments:
  RULES                 A string defining the categorization rules. Must be of
                        the form <category><maxcount>[,<category><maxcount>[,
                        ... ]]. Example: 'recent5,days12,months5'. Valid
                        <category> values: years, months, weeks, days, hours,
                        recent. Valid <maxcount> values: positive integers.
                        Default maxcount for unspecified categories: 0.
  ITEM                  Treated as path to file system entry (default) or as
                        string (--time-from-string mode). Must be omitted in
                        --stdin mode. Warning: duplicate items are treated

optional arguments:
  -h, --help            Show help message and exit.
  --extended-help       Show extended help message and exit.
  --version             Show version information and exit.
  -s, --stdin           Read items from stdin. The default separator is one
                        newline character.
  -0, --nullsep         Input and output item separator is NUL character
                        instead of newline character.
  -a, --accepted        Output accepted items and perform actions on accepted
                        items. Overrides default, which is to output rejected
                        items (and act on them).
  -t TIME, --reference-time TIME
                        Parse reference time from local time string TIME.
                        Required format is YYYYmmDD-HHMMSS. Overrides default
                        reference time, which is the time of program
  --time-from-basename FMT
                        Parse item modification time from the item path
                        basename, according to format string FMT (cf. Python's
                        strptime() docs at This overrides
                        the default behavior, which is to extract the
                        modification time from the inode.
  --time-from-string FMT
                        Treat items as strings (do not validate paths). Parse
                        time from item string using format string FMT (cf.
  -d, --delete          Attempt to delete rejected paths.
  -m DIR, --move DIR    Attempt to move rejected paths to directory DIR.
  -r, --recursive-delete
                        Enable deletion of non-empty directories.
  -v, --verbose         Control verbosity. Can be specified multiple times for
                        increasing verbosity level. Levels: error (default),
                        info, debug.

Version 0.1.0

For a detailed specification of program behavior and the time categorization method, please confer timegaps --extended-help.

General description

Timegaps’ input item set is either provided with command line arguments or read from stdin. The output is the set of rejected or accepted items, written to stdout.

Timegaps by default treats items as paths. It retrieves the modification time (st_mtime) of the corresponding file system entries via the stat system call. By default, timegaps works in a non-invasive read-only mode and simply lists the rejected (or accepted) items. If explicitly requested, timegaps can also directly delete or move the corresponding file system entries, using well- established functions from Python’s standard shutil module.

In a special mode of operation, timegaps can treat items as simple strings without path validation and extract the “modification time” from each string, according to a given time string format. This feature can be used for filtering any kind of time-dependent data, but also for filtering e.g. ZFS snapshots.

Main motivation

The well-established backup solution rsnapshot has the useful concept of hourly / daily / weekly / ... snapshots already built in and creates such a structure on the fly. Unfortunately, other backup approaches often lack such a fine-grained backup retention logic, and people tend to hack simple filters themselves. Furthermore, even rsnapshot is not able to post-process and thin out an existing set of snapshots. This is where timegaps comes in: you can use the backup solution of your choice for periodically (e.g. hourly) creating a snapshot. You can then — independently and at any time — process this set of snapshots with timegaps and identify those snapshots that need to be eliminated (removed or displaced) in order to maintain a certain “logarithmic” distribution of snapshots in time. This is the main motivation behind timegaps, but of course you can use it for filtering any kind of time-dependent data.

How can the unit tests be run?

If you run into troubles with timegaps, or if you want to verify whether it properly runs on your platform, it is a good idea to run the unit test suite under your conditions. Timegaps’ unit tests are written for pytest. With timegaps/test being the current working directory, run the tests like this:

$ py.test -v

Author & license

Timegaps is written and maintained by Jan-Philip Gehrcke. It is licensed under an MIT license (see LICENSE file).

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