circular_buffer.py

#!/bin/env/python3

class CircularBuffer:
    def __init__(self, capacity):
        self.array = [None] * capacity
        self.used = 0
        self.index = 0

    def push(self, elem):
        if self.used == len(self.array):
            return False
        self.array[(self.index + self.used) % len(self.array)] = elem
        self.used += 1
        return True

    def pop(self):
        if self.used == 0:
            raise IndexError("empty buffer")
        elem = self.array[self.index]
        self.index = (self.index + 1) % len(self.array)
        self.used -= 1
        return elem

def main():
    buf = CircularBuffer(4)
    try:
        buf.pop()
        raise AssertionError()
    except IndexError as e:
        pass
    assert buf.push(1)
    assert buf.push(2)
    assert buf.push(3)
    assert buf.push(4)
    assert not buf.push(5)
    assert buf.pop() == 1
    assert buf.pop() == 2
    assert buf.pop() == 3
    assert buf.pop() == 4

if __name__ == "__main__":
    main()