3.5.0b1: ax.contour generates different artists #20906
Description
Bug summary
The artists added when using ax.contour have changed abruptly from 3.4 to the 3.5 beta. This causes issues for workflows that use the artist properties.
Code for reproduction
import numpy as np
import matplotlib.pyplot as plt
xx, yy = np.mgrid[-3:3:.01, 0:1:.05]
zz = np.sin(xx * yy)
ax = plt.figure().subplots()
ax.contour(xx, yy, zz)
print(ax.collections[0].__class__)Actual outcome
The result on 3.5.0b1:
<class 'matplotlib.collections.PathCollection'>Expected outcome
The result on 3.4.1:
<class 'matplotlib.collections.LineCollection'>