エラー

    import matplotlib.pyplot as plt
  File "/home/ec2-user/anaconda3/lib/python3.6/site-packages/matplotlib/pyplot.py", line 115, in <module>
    _backend_mod, new_figure_manager, draw_if_interactive, _show = pylab_setup()
  File "/home/ec2-user/anaconda3/lib/python3.6/site-packages/matplotlib/backends/__init__.py", line 62, in pylab_setup
    [backend_name], 0)
  File "/home/ec2-user/anaconda3/lib/python3.6/site-packages/matplotlib/backends/backend_qt5agg.py", line 15, in <module>
    from .backend_qt5 import (
  File "/home/ec2-user/anaconda3/lib/python3.6/site-packages/matplotlib/backends/backend_qt5.py", line 19, in <module>
    import matplotlib.backends.qt_editor.figureoptions as figureoptions
  File "/home/ec2-user/anaconda3/lib/python3.6/site-packages/matplotlib/backends/qt_editor/figureoptions.py", line 20, in <module>
    import matplotlib.backends.qt_editor.formlayout as formlayout
  File "/home/ec2-user/anaconda3/lib/python3.6/site-packages/matplotlib/backends/qt_editor/formlayout.py", line 54, in <module>
    from matplotlib.backends.qt_compat import QtGui, QtWidgets, QtCore
  File "/home/ec2-user/anaconda3/lib/python3.6/site-packages/matplotlib/backends/qt_compat.py", line 140, in <module>
    from PyQt5 import QtCore, QtGui, QtWidgets
ImportError: libGL.so.1: cannot open shared object file: No such file or directory

解決策

matplotlib.pyplotインポート前に以下を宣言

import matplotlib
matplotlib.use("tkagg")
import matplotlib.pyplot as plt