The bidirectional mapping library for Python.

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  • has been used for many years by several teams at Google, Venmo, CERN, Bank of America Merrill Lynch, Bloomberg, Two Sigma, and others

  • has carefully designed APIs for safety, simplicity, flexibility, and ergonomics

  • is fast, lightweight, and has no runtime dependencies other than Python’s standard library

  • integrates natively with Python’s collections interfaces

  • is implemented in concise, well-factored, pure (PyPy-compatible) Python code optimized both for reading and learning from 1 as well as for running efficiently

  • has extensive docs and test coverage (including property-based tests and benchmarks) run continuously on all supported Python versions and OSes

Note: Python 3 Required

As promised in the 0.18.2 release (see Changelog 2), Python 2 is no longer supported. Version 0.18.3 is the last release of bidict that supports Python 2. This makes bidict more efficient on Python 3 and enables further improvement to bidict in the future. See for more info.


pip install bidict

Quick Start

>>> from bidict import bidict
>>> element_by_symbol = bidict({'H': 'hydrogen'})
>>> element_by_symbol['H']
>>> element_by_symbol.inverse['hydrogen']

For more usage documentation, head to the Introduction 3 and proceed from there.

Community Support


If you are thinking of using bidict in your work, or if you have any questions, comments, or suggestions, I’d love to know about your use case and provide as much voluntary support for it as possible.

Please feel free to leave a message in the chatroom or open a new issue on GitHub. You can search through existing issues before creating a new one in case your questions or concerns have been adressed there already.

Enterprise-Grade Support via Tidelift

Paid support available via Tidelift

If your use case requires a greater level of support, enterprise-grade support for bidict can be obtained via the Tidelift subscription.

Notice of Usage

If you use bidict, and especially if your usage or your organization is significant in some way, please let me know.

You can:


See the Changelog 2 for a history of notable changes to bidict.

Release Notifications

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Subscribe to releases on GitHub or to be notified when new versions of bidict are released.

Learning from bidict

One of the best things about bidict is that it touches a surprising number of interesting Python corners, especially given its small size and scope.

Check out Learning from bidict 1 if you’re interested in learning more.


bidict is currently a one-person operation maintained on a voluntary basis.

Your help would be most welcome!

Reviewers Wanted!

One of the most valuable ways to contribute to bidict – and to explore some interesting Python corners 1 while you’re at it – is to review the relatively small codebase.

Please create an issue or pull request with any improvements you’d propose or any other results you found. Submitting a draft PR with feedback in inline code comments, or a “Review results” issue, would each work well.

You can also +1 this issue to sign up to give feedback on future proposed changes that are in need of a reviewer.

Giving Back

bidict is the product of hundreds of hours of unpaid, voluntary work.

If bidict has helped you accomplish your work, especially work you’ve been paid for, please consider chipping in toward the costs of its maintenance and development and/or ask your organization to do the same.

Support bidict

Finding Documentation

If you’re viewing this on, note that multiple versions of the documentation are available, and you can choose a different version using the popup menu at the bottom-right. Please make sure you’re viewing the version of the documentation that corresponds to the version of bidict you’d like to use.

If you’re viewing this on GitHub, PyPI, or some other place that can’t render and link this documentation properly and are seeing broken links, try these alternate links instead:


docs/learning-from-bidict.rst |




docs/intro.rst |

Next: Introduction 3