Remove the element from a set, lists or dict.
    
        >>> L = ["Lucy"]; S = set(["Sky"]); D = { "Diamonds": True };
        >>> remove_once(L, "Lucy"); remove_once(S, "Sky"); remove_once(D, "Diamonds");
        >>> print L, S, D
        [] set([]) {}

    Returns the element if it was removed. Raises one of the exceptions in 
    :obj:`RemoveError` otherwise.

def remove_once(gset, elem):
    """Remove the element from a set, lists or dict.
    
        >>> L = ["Lucy"]; S = set(["Sky"]); D = { "Diamonds": True };
        >>> remove_once(L, "Lucy"); remove_once(S, "Sky"); remove_once(D, "Diamonds");
        >>> print L, S, D
        [] set([]) {}

    Returns the element if it was removed. Raises one of the exceptions in 
    :obj:`RemoveError` otherwise.
    """
    remove = getattr(gset, 'remove', None)
    if remove is not None: remove(elem)
    else: del gset[elem]
    return elem