Do you ever get really annoyed by problems of the rough form "shift something representable by an integer along some bounded range by some arbitrary integer, then spit out the result?" For example, the "caesar cipher" that shows up in, like, every introductory programming course ever since the beginning of time?
I know I do. So I've decided to solve it and everything of even remotely similar functional form.
Usage:
rotate(number, rotateby, top, bottom=0)
takes an initial number on a scale from top to bottom (which defaults to 0) and shifts it by rotateby. All of the arguments must be integers, and all can be positive or negative, but must satisfy top >= number >= bottom (or it throws a ValueError). Top and bottom are both included in the scale.
The mental model you should have here is of an old-school gym locker or combination padlock, where you turn the dial. Or, of course, some kind of kid's cryptography toy, with the letters represented by integers. In fact, I had an actual padlock in my hand when I wrote this code. But you can also imagine really dumb padlocks that go from, e.g., -1042 to 20. It's the really dumb stupid ones that make this code surprisingly long (just modulo won't do the trick).
The padlock I had in my hands has 40 ticks, from 0 to 39. If you have one too, you can try out the following concrete examples:
start at 5 and rotate back 10 places is equivalent to rotate(5, -10, 39, 0) and returns 35.
start at 0 and rotate forward 41 places is equivalent to rotate(0, 41, 39, 0) and returns 1. In both cases, the last
argument 0 is optional.
Also supplied in here are makeKeyFunction(rotateby, top, bottom=0) which is just a closure that returns a rotator
function tied to those specific parameters, suitable when the same rotation is to be applied to multiple numbers (e.g. in
encrypting a string); and makeRotatorFunction(top, bottom=0) which is a similar closure, but returns a function that
takes both a number and a rotateby --- or, conceptually, the rough equivalent of returning a fixed-length padlock to play
with. For example:
foo = makeKeyFunction(-10, 39, 0)
print foo(5)
bar = makeRotatorFunction(39)
print bar(5, -10)
print rotate(5, -10, 39)
will just print 35 for each print statement.
There are also test functions and such. Testing is simple: uncomment the calls to the test functions and see the joy.
Sooner or later, I'll figure out how to submit a package to pypi, and then this will actually turn into an installable module.
The code passes all the tests I could cook up for it, but all kinds of bizarre edge cases and off-by-one errors seem to like to show up when I start messing around with weird values for the parameters (especially when things go negative), and there are a few kind of klugey fixes. So if you should happen to find a test that breaks it, please do file an issue, or just fix it yourself.
written in python 2.x not 3.x, but uses future-proof integer division, so it oughta work in 3.x (with revised print statements in the tests)
The MIT License (MIT)
Copyright (c) 2015 Paul Gowder (http://paul-gowder.com)
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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