phamt

An optimized C implementation of a Persistent Hash Array Mapped Trie (PHAMT) data structure for Python.

This repository contains a C implementation for a PHAMT type. The type maps integer keys to arbitrary values efficiently, and does so with immutable/persistent data structures. It is intended for use in building more user-friendly persistent types such as persistent dictionaries and persistent lists.

Example Usage

PHAMT Usage

# The phamt library contains 2 objects: the PHAMT and THAMT classes.
>>> from phamt import PHAMT, THAMT

# The PHAMT class contains the only instance of an empty PHAMT.
>>> nothing = PHAMT.empty

# We can add key/value pairs to a PHAMT object by using the assoc method.
>>> items = nothing.assoc(42, "item 1")
>>> items = items.assoc(-3, "item 2")
>>> items = items.assoc(9999, "item 3")

# We can lookup the items just like in a normal dictionary.
>>> items[42]
"item 1"

>>> items[-3]
"item 2"

>>> items[9999]
"item 3"

# We can remove keys using the dissoc method.
>>> items = items.dissoc(9999)

>>> item.get(9999, "not found")
"not found"

# Iterate over the items.
>>> for (k,v) in items:
        print(f"key: {k}; value: {v}")
key: 42; value: item 1
key: -3; value: item 2

# PHAMTs cannot be edited, however.
>>> items[10] = 10
TypeError: 'phamt.core.PHAMT' object does not support item assignment

THAMT Usage

# The THAMT class can be created from any PHAMT. (This is O(1).)
>>> tmp = THAMT(items)

# THAMTs are also dictionaries like PHAMTs.
>>> tmp[42]
"item 1"

>>> tmp[-3]
"item 2"

# Unlike PHAMTs, THAMTs can be edited in-place. This does not modify the
# original PHAMT object.
>>> tmp[10] = 10

>>> tmp[10]
10

# THAMTs also support iteration.
>>> for (k,v) in tmp:
        print(f"key: {k}; value: {v}")
key: 42; value: item 1
key: -3; value: item 2
key: 10; value: 10

# THAMTs can be efficiently turned into PHAMTs.
>>> edited_items = tmp.persistent()

Installation

The phamt library is available on PyPI in both source and binary formats and can be installed using pip:

# Install phamt:
> pip install phamt

Current Status

PHAMT is working and is reasonably well tested overall. This includes updating PHAMTs, iterating over PHAMTs, creating PHAMTs, and querying PHAMTs. The current tests ensure that garbage collection is working correctly for deleted PHAMT components as well.

THAMT is also written and is reasonably well tested overall.

Both PHAMT and THAMT have companion Python-only implementations (see phamt.py_core), but these are not intended to be fast or space-efficient; in fact, they are a couple orders of magnitude slower than the C implementations.

License

MIT License

Copyright (c) 2022 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.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.