I came across this problem writing a custom tool for ArcGIS 10.6 and distilled it to the two lines below. import matplotlib.pyplot as plt plt.figure() When run from ArcMap, this would succeed the first time then error on subsequent attempts to import the module... File "C:\Python27\ArcGIS10.6\lib\site-packages\matplotlib\quiver.py", line 171, in <module> """ % docstring.interpd.params KeyError: u'PolyCollection' Ended up solving by repairing matplotlib using the ArcGIS Setup wizard. Not sure what may have been the cause.
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