Pyrsistent is a number of persistent collections (sometimes referred to as functional data structures). Persistent in the sense that they are immutable.

All methods on a data structure that would normally mutate it instead return a new copy of the structure containing the requested updates. The original structure is left untouched.

The collection types and key features currently implemented are:

* PVector, similar to a python list * PMap, similar to dict * PSet, similar to set * PRecord, a PMap on steroids with fixed fields, optional type and invariant checking and much more * PClass, a Python class fixed fields, optional type and invariant checking and much more * Checked collections, PVector, PMap and PSet with optional type and invariance checks and more * PBag, similar to collections.Counter * PList, a classic singly linked list * PDeque, similar to collections.deque * Immutable object type (immutable) built on the named tuple * freeze and thaw functions to convert between pythons standard collections and pyrsistent collections. * Flexible transformations of arbitrarily complex structures built from PMaps and PVectors.