'Helper function to get NDArray lists handles from various inputs.
Parameters
arg_key : str
The name of argument, used for error message.
args : list of NDArray or dict of str to NDArray
Input arguments to the symbols.
If type is list of NDArray, the position is in the same order of arg_names.
If type is dict of str to NDArray, then it maps the name of arguments
to the corresponding NDArray,
args_names : list of string
List of argument names.
allow_missing : boolean
Whether missing argument is allowed.
When allowed, the missing handle will be set to None(null)
Returns
handles : list of NDArrayHandle
The positional list of NDArrayHandles generated from input.'

@staticmethod
def _get_ndarray_inputs(arg_key, args, arg_names, allow_missing):

    arg_handles = []
    arg_arrays = []
    if isinstance(args, list):
        if (len(args) != len(arg_names)):
            raise ValueError(('Length    of    %s    does    not    match    the    number    of    arguments' % arg_key))
        for narr in args:
            if (not isinstance(narr, NDArray)):
                raise TypeError('Only    accept    list    of    NDArrays    or    dict    of    str    to    NDArray')
            arg_handles.append(narr.handle)
        arg_arrays = args
    elif isinstance(args, dict):
        for name in arg_names:
            if (name in args):
                narr = args[name]
                if (not isinstance(narr, NDArray)):
                    raise TypeError('Only    accept    list    of    NDArrays    or    dict    of    str    to    NDArray')
                arg_handles.append(narr.handle)
                arg_arrays.append(narr)
            elif allow_missing:
                arg_handles.append(None)
                arg_arrays.append(None)
            else:
                raise ValueError(('key    `%s`    is    missing    in    `%s`' % (name, arg_key)))
    else:
        raise TypeError('Only    accept    list    of    NDArrays    or    dict    of    str    to    NDArray')
    return (c_array(NDArrayHandle, arg_handles), arg_arrays)
