The sequence cannot be randomly accessed, e.g.

    In [5]: d = {1:2}

    In [6]: kv = d.keys()

    In [7]: kv
    Out[7]: dict_keys([1])

    In [8]: kv[0]
    ---------------------------------------------------------------------------
    TypeError                                 Traceback (most recent call last)
    <ipython-input-8-643f90e1910b> in <module>()
    ----> 1 kv[0]

    TypeError: 'dict_keys' object is not subscriptable

-> Use list(dict.keys()) in places where we need random access.