Circular range in Python

Question

How can I implement a circular range object in Python?

e.g.

Let S is a circular space modulo 2^3 (range [0, 2^3)). I want to generate a range object like this:

crange(3, 7, 2 ** 3)  # => a range object [3, 4, 5, 6]
crange(7, 3, 2 ** 3)  # => a range object [7, 0, 1, 2]

I tried this:

def crange(start, stop, modulo):
    if start > stop:
        return range(start, modulo) or range(stop)
    else:
        return range(start, stop)

But I can't input bigint to crange e.g. crange(8, 2, 2 ** 160).

OverflowError: Python int too large to convert to C ssize_t

Answer 1

I implemented crange which I want (in reference to @Ni and @J.F.Sebastian).

import math


class crange:
    def __init__(self, start, stop, step=None, modulo=None):
        if step == 0:
            raise ValueError('crange() arg 3 must not be zero')

        if step is None and modulo is None:
            self.start = 0
            self.stop = start
            self.step = 1
            self.modulo = stop
        else:
            self.start = start
            self.stop = stop
            if modulo is None:
                self.step = 1
                self.modulo = step
            else:
                self.step = step
                self.modulo = modulo

    def __iter__(self):
        n = self.start
        if n > self.stop:
            while n < self.modulo:
                yield n
                n += 1
            n = 0
        while n < self.stop:
            yield n
            n += 1

    def __contains__(self, n):
        if self.start >= self.stop:
            return self.start <= n < self.modulo or 0 <= n < self.stop
        else:
            return self.start <= n < self.stop

I got the following output:

>>> print(list(crange(start=7, stop=3, modulo=2 ** 4)))
[7, 8, 9, 10, 11, 12, 13, 14, 15, 0, 1, 2]
>>> print(3 in crange(start=7, stop=3, modulo=2 ** 4))
False
>>> print(7 in crange(start=7, stop=3, modulo=2 ** 4))
True
>>> print(list(crange(start=3, stop=7, modulo=2 ** 4)))
[3, 4, 5, 6]
>>> print(3 in crange(start=3, stop=7, modulo=2 ** 4))
True
>>> print(7 in crange(start=3, stop=7, modulo=2 ** 4))
False