[MacPorts] #60175: cannot import name '_tkagg' from 'matplotlib.backends' in python 2.7 and python 3.8

[MacPorts]

#60175: cannot import name '_tkagg' from 'matplotlib.backends' in python 2.7 and
python 3.8
------------------------------+-----------------------------
 Reporter:  lpagani91         |      Owner:  (none)
     Type:  defect            |     Status:  new
 Priority:  Normal            |  Milestone:
Component:  ports             |    Version:  2.6.2
 Keywords:  python libraries  |       Port:  pyxx-matplotlib
------------------------------+-----------------------------
 I have problems importing tkagg in a python program,
 though it used to work (I ran the same python program in the past):

 In [9]: matplotlib.__version__
 Out[9]: '3.1.3'
 In [10]: from matplotlib.backends.backend_tkagg import FigureCanvasTkagg
 ---------------------------------------------------------------------------
 ImportError                               Traceback (most recent call
 last)
 <ipython-input-10-b2c6c8b92aa8> in <module>
 ----> 1 from matplotlib.backends.backend_tkagg import FigureCanvasTkagg

 /opt/local/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8
 /site-packages/matplotlib/backends/backend_tkagg.py in <module>
 ----> 1 from . import _backend_tk
       2 from .backend_agg import FigureCanvasAgg
       3 from ._backend_tk import (
       4     _BackendTk, FigureCanvasTk, FigureManagerTk,
 NavigationToolbar2Tk)
       5

 /opt/local/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8
 /site-packages/matplotlib/backends/_backend_tk.py in <module>
      20 from matplotlib.figure import Figure
      21 from matplotlib.widgets import SubplotTool
 ---> 22 from . import _tkagg
      23
      24 try:

 ImportError: cannot import name '_tkagg' from 'matplotlib.backends'
 (/opt/local/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8
 /site-packages/matplotlib/backends/__init__.py)

 I searched the web but all similar problems were linked to Windows or
 Ubuntu. Tkinter was not installed in my latest Python versions so I added
 it and some people mention that I should uninstall matplotlib and
 reinstall it after having installed Tkinter but it did not help.

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Ticket URL: <https://trac.macports.org/ticket/60175>
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