class_circular.py

class CircularList(list):
    """
    A list that wraps around instead of throwing an index error.
    
    Works like a regular list:
    >>> cl = CircularList([1,2,3])
    >>> cl
    [1, 2, 3]
    
    >>> cl[0]
    1
    
    >>> cl[-1]
    3
    
    >>> cl[2]
    3
    
    Except wraps around:
    >>> cl[3]
    1
    
    >>> cl[-4]
    3
    
    Slices work
    >>> cl[0:2]
    [1, 2]
    
    but only in range.
    """
    def __getitem__(self, key):
        
        # try normal list behavior
        try:
            return super(CircularList, self).__getitem__(key)
        except IndexError:
            pass
        # key can be either integer or slice object,
        # only implementing int now.
        try:
            index = int(key)
            index = index % self.__len__()
            return super(CircularList, self).__getitem__(index)
        except ValueError:
            raise TypeError