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Async versions of the itertools features.

Project description

Async versions of the itertools features.

Example Usage

The behaviour of each feature in this project is designed to match, one-to-one, the behaviour of each feature in the Python itertools module. The primary difference of this package is that all features can additionally consume async functions and async iterables in addition to the sync versions. All functions also return async iterables.

Wrapping Sync Code

When working with sync iterables in an async world you may want to wrap things in an async interface for interoperability with other async tools. For example, a typical sync call to chain might look like:

iter1 = (1, 2, 3, 4)
iter2 = (5, 6, 7, 8)
iter3 = (9, 10, 11, 12)

for value in itertools.chain(iter1, iter2, iter3):


The above would output numbers 1 - 12 in the order shown. However, in the async world not all iterables are tuples and lists. The same thing can be accomplished with the async chain:

iter1 = (1, 2, 3, 4)
iter2 = (5, 6, 7, 8)
iter3 = (9, 10, 11, 12)

async for value in aitertools.chain(iter1, iter2, iter3):


The above behaves exactly as the sync version except that it exposes the async iteratable interface and works with async def.

Mixing Sync and Async

All functions in the aitertools package accept both sync and async iterables. This allows for the combination of the two when needed:

iter1 = (1, 2, 3, 4)
iter2 = some_async_iter()  # Async resolves to 5, 6, 7, 8

async for value in aitertools.chain(iter1, iter2):


Ensuring Async Interfaces

This package also provides a handful of tools for working with the async interfaces:

  • aiter

    Async function that counters iter. This function, when given an async iterable, will return an async iterator. When given a sync iterable it will wrap it and return an async iterator.

  • anext

    Async function that counters next. This function calls the __anext__() method of the iterator and returns the value. It, like the next method, can optionally return a default value when the iterator is empty.

  • alist

    Async function that counters list. For use cases like list(iterable) this function allows for await alist(iterable).

  • atuple

    Async function that counters tuple. Similar to the alist above.

Development Roadmap

The current release of this package is only missing the permutations, combinations, and combinations_with_replacement features. The next release should contain these missing features.

Additionally, several features from functools and the available globals are slated for addition. For example, the filter, map, and reduce features are good fits for this package and already have at least one itertools counterpart added.


All tests are stored in the ‘/tests’ subdirectory. All tests are expected to pass for Python 3.5 and above. To run tests create a virtualenv and install the test-requirements.txt list. After that using the tox command will launch the test suite.


Copyright 2015 Kevin Conway

Licensed under the Apache License, Version 2.0 (the “License”); you may not use this file except in compliance with the License. You may obtain a copy of the License at

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.


Firstly, if you’re putting in a patch then thank you! Here are some tips for getting your patch merged:


As long as the code passes the PEP8 and PyFlakes gates then the style is acceptable.


The PEP257 gate will check that all public methods have docstrings. If you’re adding additional features from the itertools module try to preserve the original docstrings if possible. Sometimes the original docs don’t fit well with the PEP257 format. In those cases it is OK to modify the docstring to fit. If you’re adding something new, like a helper function, try out the napoleon style of docstrings.


Make sure the patch passes all the tests. If you’re adding a new feature from itertools be sure to add some of the original, standard library tests. The tests used to validate the Python itertools module are found in the ‘/Lib/test/’ file in the Python source. The orginal tests are organized into large blocks of tests based on features. As much as possible, break the tests up into individual units. Check out the existing tests for this project for inspiration if needed.

If you’re adding something totally new the make sure to throw in a few tests. If you’re fixing a bug then definitely add at least one test to prevent regressions.

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