Annotate lines of a plot with matplotlib when hover with mouse

Question

I want to annotate different lines on a plot when hovering with the mouse, the same way is done here with points Possible to make labels appear when hovering over a point in matplotlib?

I tried to adapt this code as the following :

import matplotlib.pyplot as plt
import numpy as np; np.random.seed(1)
y = np.random.rand(4,15)
x = [np.arange(15) for i in range(len(y))]
names = np.array(list("ABCD"))
fig, ax = plt.subplots()
lines = []
for i in range(len(names)):
    lines.append(ax.plot(x[i],y[i]))

annot = ax.annotate("", xy=(0,0), xytext=(20,20),textcoords="offset points",
                    bbox=dict(boxstyle="round", fc="w"),
                    arrowprops=dict(arrowstyle="->"))
annot.set_visible(False)

def update_annot(ind):
    pos = line.get_offsets()[ind["ind"][0]]
    annot.xy = pos
    text = "{}, {}".format(" ".join(list(map(str,ind["ind"]))), 
                           " ".join([names[n] for n in ind["ind"]]))
    annot.set_text(text)
    annot.get_bbox_patch().set_facecolor(cmap(norm(c[ind["ind"][0]])))
    annot.get_bbox_patch().set_alpha(0.4)

def hover(event):
    vis = annot.get_visible()
    if event.inaxes == ax:
        for line in lines:
            cont, ind = line.contains(event)
            if cont:
                update_annot(ind)
                annot.set_visible(True)
                fig.canvas.draw_idle()
            else:
                if vis:
                    annot.set_visible(False)
                    fig.canvas.draw_idle()
fig.canvas.mpl_connect("motion_notify_event", hover)
plt.show()

The problem is when I hover the mouse on the plot I have the following error:

AttributeError: 'list' object has no attribute 'contains'

How can I solve this problem ?

I marked as duplicate, because that question contains two different ways of producing hovers for lines. — ImportanceOfBeingErnest, Sep 23 '19 at 10:19

score 9 · Accepted Answer · answered Sep 23 '19 at 08:38

You cannot blindly copy the code used for scatter() and use it for plot()as the returned artists are completly different.

In addition, and the root cause for the error you are seeing is that plot() returns a list of artists (even when plotting a single line). I've modified you code to give something that should be close to what you wanted like so:

import matplotlib.pyplot as plt
import numpy as np

np.random.seed(1)
y = np.random.rand(4, 15)
x = [np.arange(15) for i in range(len(y))]
names = np.array(list("ABCD"))
fig, ax = plt.subplots()
lines = []
for i in range(len(names)):
    l, = ax.plot(x[i], y[i], label=names[i])
    lines.append(l)

annot = ax.annotate("", xy=(0, 0), xytext=(20, 20), textcoords="offset points",
                    bbox=dict(boxstyle="round", fc="w"),
                    arrowprops=dict(arrowstyle="->"))
annot.set_visible(False)


def update_annot(line, idx):
    posx, posy = [line.get_xdata()[idx], line.get_ydata()[idx]]
    annot.xy = (posx, posy)
    text = f'{line.get_label()}: {posx:.2f}-{posy:.2f}'
    annot.set_text(text)
    # annot.get_bbox_patch().set_facecolor(cmap(norm(c[ind["ind"][0]])))
    annot.get_bbox_patch().set_alpha(0.4)


def hover(event):
    vis = annot.get_visible()
    if event.inaxes == ax:
        for line in lines:
            cont, ind = line.contains(event)
            if cont:
                update_annot(line, ind['ind'][0])
                annot.set_visible(True)
                fig.canvas.draw_idle()
            else:
                if vis:
                    annot.set_visible(False)
                    fig.canvas.draw_idle()


fig.canvas.mpl_connect("motion_notify_event", hover)
plt.show()

Annotate lines of a plot with matplotlib when hover with mouse

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