the code could not be run under tf2.0

[jerofree]

I try to change code “data_in = self.train_data.make_one_shot_iterator().get_next()” to “for data_in in self.train_data:”，

then below error occur.

/content/gdrive/MyDrive/Colab Notebooks/acai-master/lib/train.py:136 train  *
    for data_in in self.train_data:
/usr/local/lib/python3.7/dist-packages/tensorflow/python/autograph/operators/control_flow.py:422 for_stmt
    iter_, extra_test, body, get_state, set_state, symbol_names, opts)
/usr/local/lib/python3.7/dist-packages/tensorflow/python/autograph/operators/control_flow.py:727 _tf_dataset_for_stmt
    _verify_loop_init_vars(init_vars, symbol_names)
/usr/local/lib/python3.7/dist-packages/tensorflow/python/autograph/operators/control_flow.py:191 _verify_loop_init_vars
    raise ValueError(error_msg)

ValueError: 'self.sess' may not be None before the loop.