Bug report

Bug summary
pyplot.stem does not support subclasses of numpy.ndarray that have defined the matplotlib.units.ConversionInterface. In the example below, I am using the unyt library where unyt_array is a np.ndarray subclass and the library has defined the units.ConversionInterface. pyplot.plot works as expected, but pyplot.stem never calls the ConversionInterface.

The problem is in _axes.py in the first line of pyplot.stem where y = np.asarray(y) converts the unyt_array to a pure np.ndarray and the subsequent line y = self.convert_yunits(y) never calls the ConversionInterface because y is now a np.ndarray. Changing the first line to y = np.asanyarray(y) fixes the problem allowing the subclass to pass through.

Is it possible for matplotlib to update pyplot.stem to support np.ndarray subclasses?

Code for reproduction

>>> import matplotlib.pyplot as plt
>>> import unyt
>>> unyt.matplotlib_support()
>>> y = unyt.unyt_array([1,2,3], "m", name="length")
>>> fig, ax = plt.subplots()
>>> ax.stem(y)
>>> ax.yaxis.get_label().get_text()

Actual outcome

''

Expected outcome

'$\\left(\\rm{m}\\right)$'

Matplotlib version

• Operating system: Linux
• Matplotlib version: 3.1.2
• Matplotlib backend (print(matplotlib.get_backend())): TkAgg
• Python version: 3.6.9
• Jupyter version (if applicable):
• Other libraries: unyt: 2.6.0