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 many 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 interfaces

  • provides type hints for all public APIs

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

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


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.

Enterprise Support

Enterprise-level support for bidict can be obtained via the Tidelift subscription or by contacting me directly.

I have a US-based LLC set up for invoicing, and I have 15+ years of professional experience delivering software and support to companies successfully.

You can also sponsor my work through platforms like GitHub Sponsors. See the Sponsoring section below for details. For rationale and examples of companies doing this, see this post among others.

Voluntary Community Support

Please search through already-asked questions and answers in GitHub Discussions and the issue tracker in case your question has already been addressed.

Otherwise, please feel free to start a new discussion or create a new issue on GitHub, or ask in the bidict chatroom for voluntary community support.

Notice of Usage

If you use bidict, and especially if your usage or your organization is significant in some way, please let me know in any of the following ways:


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

Release Notifications

Watch releases on GitHub 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.


I have been bidict’s sole maintainer and active contributor since I started the project almost 15 years ago.

Your help would be most welcome! See the Contributors’ Guide 4 for more information.


Sponsor through GitHub

Bidict is the product of thousands of hours of my unpaid work over the ~15 years that I’ve been the sole maintainer.

If bidict has helped you or your company accomplish your work, especially work that you or your company were paid for, please sponsor my work through GitHub, and ask others you know who got value from my work to do the same.

Choose a tier and GitHub handles everything else. Sponsorship just goes on the same bill that GitHub already charges you or your company for automatically, so after the one-time signup, there’s nothing extra to do.

You can also sponsor my work through Gumroad or PayPal, or through a support engagement with my LLC. See Enterprise Support above for details.

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 |


docs/contributors-guide.rst |

Next: Introduction 3