绘制“plot”而不是“scatter”时，图例选择会中断

再会。这个问题是后续问题为什么图例选取仅适用于“ax.twinx()”而不适用于“ax”？ https://stackoverflow.com/q/60167378/9282844.

下面提供的最小代码分别绘制了两条曲线ax1 and ax2 = ax1.twinx()，它们的图例框被创建，底部图例被移动到顶轴，以便可以使用选择器事件。单击图例项将隐藏/显示关联的曲线。

If ax.scatter(...)使用效果很好。If ax.plot(...)改为使用，图例选取突然中断。为什么？没有其他任何改变，所以这很令人困惑。我测试了其他几种绘图方法，但没有一个按预期工作。

这是一个实际操作的视频：https://imgur.com/qsPYHKc.mp4 https://imgur.com/qsPYHKc.mp4

import matplotlib.pyplot as plt
import numpy as np

fig, ax1 = plt.subplots()
ax2 = ax1.twinx()

X = np.linspace(0, 2*np.pi, 100)
Y1 = X**0.5 * np.sin(X)
Y2 = -np.cos(X)

# This is a quick way to change the plotting function, simply modify n.
n = 0
function, container = [("scatter", "collections"),
                       ("plot",    "lines"),
                       ("bar",     "patches"),
                       ("barbs",   "collections"),
                       ("quiver",  "collections")][n]
getattr(ax1, function)(X, Y1, color="green", label="$Y_1$")
getattr(ax2, function)(X, Y2, color="red",   label="$Y_2$")

# Put both legends on ax2 so that pick events also work for ax1's legend.
legend1 = ax1.legend(loc="upper left")
legend2 = ax2.legend(loc="upper right")
legend1.remove()
ax2.add_artist(legend1)

for n, legend in enumerate((legend1, legend2)):
    legend_item = legend.legendHandles[0]
    legend_item.set_gid(n+1)
    legend_item.set_picker(10)

# When a legend element is picked, hide/show the associated curve.   
def on_graph_pick_event(event):

    gid = event.artist.get_gid()
    print(f"Picked Y{gid}'s legend.")

    ax = {1: ax1, 2: ax2}[gid]
    for artist in getattr(ax, container):
        artist.set_visible(not artist.get_visible())
    plt.draw()

fig.canvas.mpl_connect("pick_event", on_graph_pick_event)

好吧，我知道这不是答案，但评论不允许我进行这种头脑风暴。我尝试了几件事，并注意到以下内容。当您打印axes of the legendHandles艺术家在你的 for 循环中，它返回None对于散点图的两个图例 /PathCollection艺术家。然而，在“正常”情节的情况下/Line2D艺术家，它返回轴对象！甚至还不止于此；即使在终端中它们的表示似乎是相同的（AxesSubplot(0.125,0.11;0.775x0.77)），如果你检查它们是否是== ax2， 为了legendHandles的艺术家legend1它返回False，而对于其中之一legend2，它返回True。这里发生了什么？

所以我不仅尝试删除legend1 from ax1并再次添加到ax2但也对legendHandles目的。但它不允许我这样做：

NotImplementedError: cannot remove artist

在我看来，您似乎发现了一个错误，或者至少发现了不一致的行为。这是我到目前为止尝试过的代码，以防其他人想进一步尝试。

import matplotlib.pyplot as plt
import matplotlib
matplotlib.use('Qt5Agg')
import numpy as np

fig, ax1 = plt.subplots()
ax2 = ax1.twinx()

X = np.linspace(0, 2*np.pi, 100)
Y1 = X**0.5 * np.sin(X)
Y2 = -np.cos(X)

USE_LINES = True  # <--- set this to True or False to test both cases.
if USE_LINES:
    ax1.plot(X, Y1, color="green", label="$Y_1$")
    ax2.plot(X, Y2, color="red",   label="$Y_2$")
else:
    ax1.scatter(X, Y1, color="green", label="$Y_1$")
    ax2.scatter(X, Y2, color="red",   label="$Y_2$")

# Put both legends on ax2 so that pick events also work for ax1's legend.
legend1 = ax1.legend(loc="upper left")
legend2 = ax2.legend(loc="upper right")
legend1.remove()
ax2.add_artist(legend1)
# legend1.legendHandles[0].remove()
# ax2.add_artist(legend1.legendHandles[0])

for n, legend in enumerate((legend1, legend2)):
    legend_item = legend.legendHandles[0]
    legend_item.set_gid(n+1)
    legend_item.set_picker(10)
    print(
        f'USE_LINES = {USE_LINES}', f'legend{n+1}',
        legend_item.axes.__repr__() == legend.axes.__repr__(),
        legend_item.axes == legend.axes,
        legend_item.axes.__repr__() == ax2.__repr__(),
        legend_item.axes == ax2, type(legend_item),
    )

# When a legend element is picked, hide/show the associated curve.
def on_graph_pick_event(event):

    gid = event.artist.get_gid()
    print(f"Picked Y{gid}'s legend.")

    ax = {1: ax1, 2: ax2}[gid]
    artist = ax.lines[0] if USE_LINES else ax.collections[0]
    artist.set_visible(not artist.get_visible())
    plt.draw()

fig.canvas.mpl_connect("pick_event", on_graph_pick_event)
plt.show()