pcollections

pcollections

A persistent collections library for Python.

About

pcollections is a library of persistent (immutable) collections inspired by the immutable data structures of Clojure but built to resemble the native Python collections as closely as possible. The library is implemented in Python but employs the phamt (Persistent Hash Array Mapped Tries) library, which is implemented in C, to perform efficient low-level operations.

The library implements three persistent types: plist, pset, and pdict. These are immutable versions of the builtin list, set, and dict types. The persistent object interfaces are as similar as possible to the native types, but the method signatures differ in ways necessary to accomodate efficient immutable ways of doing things. For example, the pdict constructor is identical to the dict constructor and always returns a pdict equal to the dict that would be created with the same arguments. However, instead of supporting operations like d[key] = val, pdicts support a set method: d = d.set(key, val).

In addition to the persistent types, there are two lazy types, llist and ldict. These types are enabled by the lazy type. A lazy object is basically a partial object that, when called, caches the function's return value and returns that value without rerunning the function on subsequent calls. The llist and ldict types are equivalent to the plist and pdict types with one exception. Elements of an llist and values of an ldict that are of the lazy type are dereferenced when requested. This allows a programmer to easily create data structures (potentially nested data structures) whose items are the results of complex or long-running computations that only get computed once requested. The persistent data structures allow the arguments to these lazy functions to be safe from mutation.

Finally, the persistent and lazy types have transient correlaries that enable more efficient batch-mutation of the persistent types. The transient types tlist, tset, tdict, tllist, and tldict all have interfaces equivalent to their standard mutable correlaries (transient types are mutable).

License

MIT License

Copyright (c) 2022-2023 Noah C. Benson

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

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