Sum walker. Iterate over sums of a certain number of elements

Info

This is the README file for Sum walker.

Author

Shlomi Fish <shlomif@cpan.org>

Copyright

© 2020, Shlomi Fish.

Date

2020-02-25

Version

0.8.2

https://travis-ci.org/shlomif/sum_walker.svg?branch=master

PURPOSE

The sum_walker PyPI distribution allows one to iterate over increasing sums of a certain number (e.g: 2 or 3) of elements out of a stream of increasing integers.

INSTALLATION

pip3 install sum_walker

USAGE

A simple example of printing sums of two integers:

#! /usr/bin/env python3
# -*- coding: utf-8 -*-
# vim:fenc=utf-8
#
# Copyright © 2020 Shlomi Fish <shlomif@cpan.org>
#
# Distributed under the terms of the MIT license.
#
# This program displays increasing sums of two positive integers

from six import print_
import sum_walker.iterator_wrapper


def main():
    def natural_nums_iter():
        ret = 1
        while True:
            yield ret
            ret += 1

    walker = sum_walker.iterator_wrapper.Walker(
        counts=[2], iterator=natural_nums_iter())

    def print_next():
        nonlocal walker
        sum_, coords = next(walker)
        print_("{} = {}".format(
            sum_, " ; ".join(
                [" + ".join([str(x.value) for x in permutation])
                 for permutation in coords])))

    # Prints «2 = 1 + 1»
    print_next()

    # Prints «3 = 1 + 2»
    print_next()

    # Prints «4 = 1 + 3 ; 2 + 2»
    print_next()

    # Prints «5 = 1 + 4 ; 2 + 3»
    print_next()

    # Prints «6 = 1 + 5 ; 2 + 4 ; 3 + 3»
    print_next()

main()

A more interesting example, this time using the more beaurocratic sum_walker module:

# Finding sums of two powers of 3 (= i**3 ) in two or more
# different ways:
#
# https://en.wikipedia.org/wiki/Taxicab_number
from sum_walker import DWIM_SumWalker

seq = [0, 1]
reached = 2

def request_more():
    nonlocal reached
    nonlocal seq
    seq.append(reached ** 3)
    reached += 1

it = DWIM_SumWalker(2, seq, request_more)
for sum_, coords in it:
    len_ = len(coords)
    if len_ > 1:
        print("{}\t{}\t{}".format(
            len_, sum_, " ; ".join(
                [" + ".join(["{} ** 3".format(x) for x in c])
                 for c in coords])))

NOTES