today's python error

# python train.py
../common/trainer.py:7: UserWarning: 
This call to matplotlib.use() has no effect because the backend has already
been chosen; matplotlib.use() must be called *before* pylab, matplotlib.pyplot,
or matplotlib.backends is imported for the first time.

The backend was *originally* set to 'Qt5Agg' by the following code:
  File "train.py", line 5, in <module>
    import matplotlib.pyplot as plt
  File "/opt/conda/lib/python3.6/site-packages/matplotlib/pyplot.py", line 71, in <module>
    from matplotlib.backends import pylab_setup
  File "/opt/conda/lib/python3.6/site-packages/matplotlib/backends/__init__.py", line 16, in <module>
    line for line in traceback.format_stack()


  mpl.use('Agg')
Traceback (most recent call last):
  File "train.py", line 12, in <module>
    from ch07.peeky_seq2seq import PeekySeq2seq
  File "../ch07/peeky_seq2seq.py", line 5, in <module>
    from seq2seq import Seq2seq, Encoder
ModuleNotFoundError: No module named 'seq2seq'

# python visualize_attention.py 
Traceback (most recent call last):
  File "visualize_attention.py", line 60, in <module>
    visualize(attention_map, row_labels, column_labels)
  File "visualize_attention.py", line 26, in visualize
    fig, ax = plt.subplots()
  File "/opt/conda/lib/python3.6/site-packages/matplotlib/pyplot.py", line 1198, in subplots
    fig = figure(**fig_kw)
  File "/opt/conda/lib/python3.6/site-packages/matplotlib/pyplot.py", line 548, in figure
    **kwargs)
  File "/opt/conda/lib/python3.6/site-packages/matplotlib/backend_bases.py", line 161, in new_figure_manager
    return cls.new_figure_manager_given_figure(num, fig)
  File "/opt/conda/lib/python3.6/site-packages/matplotlib/backend_bases.py", line 167, in new_figure_manager_given_figure
    canvas = cls.FigureCanvas(figure)
  File "/opt/conda/lib/python3.6/site-packages/matplotlib/backends/backend_qt5agg.py", line 24, in __init__
    super(FigureCanvasQTAgg, self).__init__(figure=figure)
  File "/opt/conda/lib/python3.6/site-packages/matplotlib/backends/backend_qt5.py", line 234, in __init__
    _create_qApp()
  File "/opt/conda/lib/python3.6/site-packages/matplotlib/backends/backend_qt5.py", line 125, in _create_qApp
    raise RuntimeError('Invalid DISPLAY variable')
RuntimeError: Invalid DISPLAY variable