commit 6e83111276f99464aaa908a2c5d776b70aa64888 Author: Brandon Rozek Date: Sun Oct 11 21:44:15 2020 -0400 Initial Commit diff --git a/README.md b/README.md new file mode 100644 index 0000000..ebaca60 --- /dev/null +++ b/README.md @@ -0,0 +1,59 @@ +# tail_recurse: Tail Call Optimization Decorator for Python + +This library adds the ability to perform tail call optimizations in your Python code with the addition of a decorator. + +Blog Post: https://brandonrozek.com/blog/tcopython/ + +This code is heavily inspired by Crutcher Dunnavant's [code snippet](https://code.activestate.com/recipes/474088-tail-call-optimization-decorator/) from 2006. + +## Installation + +```bash +pip install tail-recurse +``` + +## Usage + +### Factorial + +Definition: + +```python +@tail_call +def factorial(n, acc=1): + if n == 0: + return acc + return factorial(n - 1, n * acc) +``` + +Usage: + +```python +>>> factorial(1000) +402387260077093773543702433923003985719374864210714632543799910429938512398629020592044208486969404800479988610197196058631666872994808558901323829669944590997424504087073759918823627727188732519779505950995276120874975462497043601418278094646496291056393887437886487337119181045825783647849977012476632889835955735432513185323958463075557409114262417474349347553428646576611667797396668820291207379143853719588249808126867838374559731746136085379534524221586593201928090878297308431392844403281231558611036976801357304216168747609675871348312025478589320767169132448426236131412508780208000261683151027341827977704784635868170164365024153691398281264810213092761244896359928705114964975419909342221566832572080821333186116811553615836546984046708975602900950537616475847728421889679646244945160765353408198901385442487984959953319101723355556602139450399736280750137837615307127761926849034352625200015888535147331611702103968175921510907788019393178114194545257223865541461062892187960223838971476088506276862967146674697562911234082439208160153780889893964518263243671616762179168909779911903754031274622289988005195444414282012187361745992642956581746628302955570299024324153181617210465832036786906117260158783520751516284225540265170483304226143974286933061690897968482590125458327168226458066526769958652682272807075781391858178889652208164348344825993266043367660176999612831860788386150279465955131156552036093988180612138558600301435694527224206344631797460594682573103790084024432438465657245014402821885252470935190620929023136493273497565513958720559654228749774011413346962715422845862377387538230483865688976461927383814900140767310446640259899490222221765904339901886018566526485061799702356193897017860040811889729918311021171229845901641921068884387121855646124960798722908519296819372388642614839657382291123125024186649353143970137428531926649875337218940694281434118520158014123344828015051399694290153483077644569099073152433278288269864602789864321139083506217095002597389863554277196742822248757586765752344220207573630569498825087968928162753848863396909959826280956121450994871701244516461260379029309120889086942028510640182154399457156805941872748998094254742173582401063677404595741785160829230135358081840096996372524230560855903700624271243416909004153690105933983835777939410970027753472000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 + +``` + +### Fibonacci Numbers + +Definition: + +```python +@tail_call +def fib(n, a=0, b=1): + if n == 0: + return a + if n == 1: + return b + return fib(n - 1, b, a + b) +``` + +Usage: + +```python +>>> fib(1000) +43466557686937456435688527675040625802564660517371780402481729089536555417949051890403879840079255169295922593080322634775209689623239873322471161642996440906533187938298969649928516003704476137795166849228875 +``` + + + diff --git a/setup.py b/setup.py new file mode 100644 index 0000000..1b95bcf --- /dev/null +++ b/setup.py @@ -0,0 +1,23 @@ +import setuptools + +with open("README.md", "r") as fh: + long_description = fh.read() + +setuptools.setup( + name="tail-recurse", + version="0.1", + author="Brandon Rozek", + author_email="hello@brandonrozek.com", + description="Tail Call Optimization Decorator for Python.", + long_description=long_description, + long_description_content_type="text/markdown", + url="https://github.com/brandon-rozek/tail-recurse", + packages=setuptools.find_packages(), + classifiers=[ + "Programming Language :: Python :: 3", + "License :: OSI Approved :: MIT License", + "Operating System :: OS Independent", + ], + python_requires='>=3.7', +) + diff --git a/tail_recurse/__init__.py b/tail_recurse/__init__.py new file mode 100644 index 0000000..ceffa99 --- /dev/null +++ b/tail_recurse/__init__.py @@ -0,0 +1,40 @@ +""" +Python Decorator that enables tail call +optimization through Exception Trampolines. +""" +from dataclasses import dataclass, field +from typing import Any, Dict, List +import functools +import inspect + +@dataclass +class TailRecurseException(Exception): + """Exception to enable tail call recursion.""" + args: List[Any] = field(default_factory=list) + kwargs: Dict[Any, Any] = field(default_factory=dict) + +def tail_call(func): + """ + Decorator that performs tail call optimization. + + Notes + ===== + Works by throwing an exception to exit the stack + when the function sees itself as its grandparent in + the stack trace. It then calls itself with its new + arguments. + """ + @functools.wraps(func) + def recurse(*args, **kwargs): + frame = inspect.currentframe() + if frame.f_back is not None \ + and frame.f_back.f_back is not None \ + and frame.f_back.f_back.f_code == frame.f_code: + raise TailRecurseException(args, kwargs) + while True: + try: + return func(*args, **kwargs) + except TailRecurseException as exception: + args = exception.args + kwargs = exception.kwargs + return recurse