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More routines for operating on iterables, beyond itertools

Project description

Python’s itertools library is a gem - you can compose elegant solutions for a variety of problems with the functions it provides. In more-itertools we collect additional building blocks, recipes, and routines for working with Python iterables.

Grouping chunked, ichunked, sliced, distribute, divide, split_at, split_before, split_after, split_into, split_when, bucket, unzip, grouper, partition
Lookahead and lookback spy, peekable, seekable
Windowing windowed, substrings, substrings_indexes, stagger, windowed_complete, pairwise
Augmenting count_cycle, intersperse, padded, mark_ends, repeat_last, adjacent, groupby_transform, padnone, ncycles
Combining collapse, sort_together, interleave, interleave_longest, zip_offset, zip_equal, dotproduct, convolve, flatten, roundrobin, prepend, value_chain
Summarizing ilen, unique_to_each, sample, consecutive_groups, run_length, map_reduce, exactly_n, is_sorted, all_equal, all_unique, first_true, quantify
Selecting islice_extended, first, last, one, only, strip, lstrip, rstrip, filter_except map_except nth_or_last, nth, take, tail, unique_everseen, unique_justseen
Combinatorics distinct_permutations, distinct_combinations, circular_shifts, partitions, set_partitions, product_index, combination_index, permutation_index, powerset, random_product, random_permutation, random_combination, random_combination_with_replacement, nth_product nth_permutation nth_combination
Wrapping always_iterable, always_reversible, consumer, with_iter, iter_except
Others locate, rlocate, replace, numeric_range, side_effect, iterate, difference, make_decorator, SequenceView, time_limited, consume, tabulate, repeatfunc

Getting started

To get started, install the library with pip:

pip install more-itertools

The recipes from the itertools docs are included in the top-level package:

>>> from more_itertools import flatten
>>> iterable = [(0, 1), (2, 3)]
>>> list(flatten(iterable))
[0, 1, 2, 3]

Several new recipes are available as well:

>>> from more_itertools import chunked
>>> iterable = [0, 1, 2, 3, 4, 5, 6, 7, 8]
>>> list(chunked(iterable, 3))
[[0, 1, 2], [3, 4, 5], [6, 7, 8]]

>>> from more_itertools import spy
>>> iterable = (x * x for x in range(1, 6))
>>> head, iterable = spy(iterable, n=3)
>>> list(head)
[1, 4, 9]
>>> list(iterable)
[1, 4, 9, 16, 25]

For the full listing of functions, see the API documentation.


more-itertools is maintained by @erikrose and @bbayles, with help from many others. If you have a problem or suggestion, please file a bug or pull request in this repository. Thanks for contributing!

Version History



  • New functions
    • convolve (from the Python itertools docs)
    • product_index, combination_index, and permutation_index (thanks to N8Brooks)
    • value_chain (thanks to jenstroeger)
  • Changes to existing functions
    • distinct_combinations now uses a non-recursive algorithm (thanks to knutdrand)
    • pad_none is now the preferred name for padnone, though the latter remains available.
    • pairwise will now use the Python standard library implementation on Python 3.10+
    • sort_together now accepts a key argument (thanks to brianmaissy)
    • seekable now has a peek method, and can indicate whether the iterator it’s wrapping is exhausted (thanks to gsakkis)
    • time_limited can now indicate whether its iterator has expired (thanks to roysmith)
    • The implementation of unique_everseen was improved (thanks to plammens)
  • Other changes:
    • Various documentation updates (thanks to cthoyt, Evantm, and cyphase)


  • New itertools
    • all_unique (thanks to brianmaissy)
    • nth_product and nth_permutation (thanks to N8Brooks)
  • Changes to existing itertools
    • chunked and sliced now accept a strict parameter (thanks to shlomif and jtwool)
  • Other changes
    • Python 3.5 has reached its end of life and is no longer supported.
    • Python 3.9 is officially supported.
    • Various documentation fixes (thanks to timgates42)


  • New itertools
    • windowed_complete (thanks to MarcinKonowalczyk)
  • Changes to existing itertools:
    • The is_sorted implementation was improved (thanks to cool-RR)
    • The groupby_transform now accepts a reducefunc parameter.
    • The last implementation was improved (thanks to brianmaissy)
  • Other changes
    • Various documentation fixes (thanks to craigrosie, samuelstjean, PiCT0)
    • The tests for distinct_combinations were improved (thanks to Minabsapi)
    • Automated tests now run on GitHub Actions. All commits now check:
      • That unit tests pass
      • That the examples in docstrings work
      • That test coverage remains high (using coverage)
      • For linting errors (using flake8)
      • For consistent style (using black)
      • That the type stubs work (using mypy)
      • That the docs build correctly (using sphinx)
      • That packages build correctly (using twine)


  • New itertools
    • mark_ends (thanks to kalekundert)
    • is_sorted
  • Changes to existing itertools:
    • islice_extended can now be used with real slices (thanks to cool-RR)
    • The implementations for filter_except and map_except were improved (thanks to SergBobrovsky)
  • Other changes
    • Automated tests now enforce code style (using black)
    • The various signatures of islice_extended and numeric_range now appear in the docs (thanks to dsfulf)
    • The test configuration for mypy was updated (thanks to blueyed)


  • New itertools
    • zip_equal (thanks to frankier and alexmojaki)
  • Changes to existing itertools:
    • split_at, split_before, split_after, and split_when all got a maxsplit paramter (thanks to jferard and ilai-deutel)
    • split_at now accepts a keep_separator parameter (thanks to jferard)
    • distinct_permutations can now generate r-length permutations (thanks to SergBobrovsky and ilai-deutel)
    • The windowed implementation was improved (thanks to SergBobrovsky)
    • The spy implementation was improved (thanks to has2k1)
  • Other changes
    • Type stubs are now tested with stubtest (thanks to ilai-deutel)
    • Tests now run with python -m unittest instead of python test (thanks to jdufresne)


  • Bug fixes
    • The .pyi files for typing were updated. (thanks to blueyed and ilai-deutel)
  • Changes to existing itertools:
    • numeric_range now behaves more like the built-in range. (thanks to jferard)
    • bucket now allows for enumerating keys. (thanks to alexchandel)
    • sliced now should now work for numpy arrays. (thanks to sswingle)
    • seekable now has a maxlen parameter.


  • Bug fixes
    • partition works with pred=None again. (thanks to MSeifert04)
  • New itertools
    • sample (thanks to tommyod)
    • nth_or_last (thanks to d-ryzhikov)
  • Changes to existing itertools:
    • The implementation for divide was improved. (thanks to jferard)


  • Bug fixes
    • The type stub files are now part of the wheel distribution (thanks to keisheiled)


  • Bug fixes
    • The type stub files now work for functions imported from the root package (thanks to keisheiled)


  • New itertools and other additions
    • This library now ships type hints for use with mypy. (thanks to ilai-deutel for the implementation, and to gabbard and fmagin for assistance)
    • split_when (thanks to jferard)
    • repeat_last (thanks to d-ryzhikov)
  • Changes to existing itertools:
    • The implementation for set_partitions was improved. (thanks to jferard)
    • partition was optimized for expensive predicates. (thanks to stevecj)
    • unique_everseen and groupby_transform were re-factored. (thanks to SergBobrovsky)
    • The implementation for difference was improved. (thanks to Jabbey92)
  • Other changes
    • Python 3.4 has reached its end of life and is no longer supported.
    • Python 3.8 is officially supported. (thanks to jdufresne)
    • The collate function has been deprecated. It raises a DeprecationWarning if used, and will be removed in a future release.
    • one and only now provide more informative error messages. (thanks to gabbard)
    • Unit tests were moved outside of the main package (thanks to jdufresne)
    • Various documentation fixes (thanks to kriomant, gabbard, jdufresne)


  • New itertools
    • distinct_combinations
    • set_partitions (thanks to kbarrett)
    • filter_except
    • map_except


  • New itertools
    • ichunked (thanks davebelais and youtux)
    • only (thanks jaraco)
  • Changes to existing itertools:
    • numeric_range now supports ranges specified by datetime.datetime and datetime.timedelta objects (thanks to MSeifert04 for tests).
    • difference now supports an initial keyword argument.
  • Other changes
    • Various documentation fixes (thanks raimon49, pylang)


  • New itertools:
    • time_limited
    • partitions (thanks to rominf and Saluev)
    • substrings_indexes (thanks to rominf)
  • Changes to existing itertools:
    • collapse now treats bytes objects the same as str objects. (thanks to Sweenpet)

The major version update is due to the change in the default behavior of collapse. It now treats bytes objects the same as str objects. This aligns its behavior with always_iterable.

>>> from more_itertools import collapse
>>> iterable = [[1, 2], b'345', [6]]
>>> print(list(collapse(iterable)))
[1, 2, b'345', 6]


  • Major changes:
    • Python 2.7 is no longer supported. The 5.0.0 release will be the last version targeting Python 2.7.
    • All future releases will target the active versions of Python 3. As of 2019, those are Python 3.4 and above.
    • The six library is no longer a dependency.
    • The accumulate function is no longer part of this library. You may import a better version from the standard itertools module.
  • Changes to existing itertools:
    • The order of the parameters in grouper have changed to match the latest recipe in the itertools documentation. Use of the old order will be supported in this release, but emit a DeprecationWarning. The legacy behavior will be dropped in a future release. (thanks to jaraco)
    • distinct_permutations was improved (thanks to jferard - see also permutations with unique values at StackOverflow.)
    • An unused parameter was removed from substrings. (thanks to pylang)
  • Other changes:
    • The docs for unique_everseen were improved. (thanks to jferard and MSeifert04)
    • Several Python 2-isms were removed. (thanks to jaraco, MSeifert04, and hugovk)

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