[Debian-med-packaging] Bug#896330: python-matplotlib-venn: matplotlib_venn fails to import

[Helmut Grohne]

Package: python-matplotlib-venn
Version: 0.11.5-3
Severity: serious
User: helmutg at debian.org
Usertags: python-import

After installing python-matplotlib-venn importing the module matplotlib_venn
into a python interpreter fails with the following error:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib/python2.7/dist-packages/matplotlib_venn/__init__.py", line 55, in <module>
    from matplotlib_venn._venn2 import venn2, venn2_circles
  File "/usr/lib/python2.7/dist-packages/matplotlib_venn/_venn2.py", line 22, in <module>
    from matplotlib.pyplot import gca
  File "/usr/lib/python2.7/dist-packages/matplotlib/pyplot.py", line 115, in <module>
    _backend_mod, new_figure_manager, draw_if_interactive, _show = pylab_setup()
  File "/usr/lib/python2.7/dist-packages/matplotlib/backends/__init__.py", line 62, in pylab_setup
    [backend_name], 0)
  File "/usr/lib/python2.7/dist-packages/matplotlib/backends/backend_tkagg.py", line 4, in <module>
    from . import tkagg  # Paint image to Tk photo blitter extension.
  File "/usr/lib/python2.7/dist-packages/matplotlib/backends/tkagg.py", line 5, in <module>
    from six.moves import tkinter as Tk
  File "/usr/lib/python2.7/dist-packages/six.py", line 203, in load_module
    mod = mod._resolve()
  File "/usr/lib/python2.7/dist-packages/six.py", line 115, in _resolve
    return _import_module(self.mod)
  File "/usr/lib/python2.7/dist-packages/six.py", line 82, in _import_module
    __import__(name)
  File "/usr/lib/python2.7/lib-tk/Tkinter.py", line 42, in <module>
    raise ImportError, str(msg) + ', please install the python-tk package'
ImportError: No module named _tkinter, please install the python-tk package

The vast majority of import failures is attributed to missing dependencies.
Often times that manifests as an ImportError or ModuleNotFoundError.
Typically, dependencies should be inserted by dh-python via ${python:Depends}
or ${python3:Depends}. Thus a missing dependency can be caused by incomplete
install_requires in setup.py. Sometimes a missing dependency of a dependency
is the cause, in such cases this bug should be reassigned.

Helmut