Created by: Aurelius84

In this PR, we support to modify dict and list in while_loop.

You can write code as followed:

def cond(i, ten, test_dict, test_list, test_list_dict):
    return layers.less_than(i, ten)

def body(i, ten, test_dict, test_list, test_list_dict):
    # Modify the tensor by python dict syntax.
    test_dict["test_key"] = i
    test_dict["test_key"] += 1

    test_list[0] = fluid.layers.reshape(test_list[0], [2, -1]) + 1

    test_list_dict[0]["test_key"] += 1
    test_list_dict[0]["test_key"] = fluid.layers.relu(test_list_dict[0][
        "test_key"])

    i = layers.increment(i)
    return [i, ten, test_dict, test_list, test_list_dict]

main_program = Program()
startup_program = Program()
with program_guard(main_program, startup_program):
    i = layers.zeros(shape=[1], dtype='int64')
    ten = layers.fill_constant(shape=[1], dtype='int64', value=10)
    test_data = layers.fill_constant(shape=[1], dtype='int64', value=0)
    # Define list/dict that holds tensor
    test_dict = {"test_key": test_data}
    test_list = [layers.fill_constant(shape=[1, 2], dtype='int64', value=0)]
    test_list_dict = [{"test_key": layers.fill_constant(shape=[1], dtype='float32', value=0)}]

    i, ten, test_dict, test_list, test_list_dict = layers.while_loop(cond, body, [i, ten, test_dict, test_list, test_list_dict])