Efficient, Pythonic bidirectional map implementation and related functionality.

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  • is in use 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 CPython-, PyPy-, Python 2-, and Python 3-compatible

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

  • integrates natively with Python’s collections interfaces

  • is implemented in concise, well-factored, well-documented pure Python that leverages a number of advanced language features 3

⚠️ Python 2 EOL ⚠️

Python 2 support will be dropped in a future release.

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 1 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.

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 bidict releases on to be notified when new versions of bidict are released. Alternatively, on GitHub, click “Watch” and choose “Releases”.

Learning from bidict

One of the most rewarding things about bidict is the outsized amount of advanced Python it covers in light of its small codebase.

Check out Learning from bidict 3 if you’re interested in learning more.


Bidict is currently a one-person operation maintained on a voluntary basis with no other sponsorship. Your help would be most welcome!

Reviewers Wanted!

One of the most valuable ways to contribute to bidict and to explore some advanced Python 3 while you’re at it is to review bidict’s relatively small codebase.

Please create an issue or pull request with any improvements you’d propose or any other results you found. (Submitting a “Nothing-to-merge” PR with feedback in inline code comments or a Review results issue both 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 bidict’s 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/intro.rst |




docs/learning-from-bidict.rst |

Next: Introduction 1