def bizect(l, steps="a"):
    """
    given a list, select the a/b n-th group plus the last element 

    >>> l = list(range(10))
    >>> bizect(l)                                                                                                                                            
    [0, 1, 2, 3, 4, 9]
    >>> bizect(l, steps="b")                                                                                                                                            
    [5, 6, 7, 8, 9]
    >>> bizect(l, "ba")                                                                                                                                      
    [5, 6, 9]
    >>> bizect(l, "bb")                                                                                                                                      
    [7, 8, 9]
    """
    r = l.copy()
    for key in steps:
        if key == "a":
            r = r[:len(r)//2]
        else: 
            r = r[len(r)//2:-1]
        r += [l[-1]]
    return r