The bidirectional mapping library for Python.


  • 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']