交互：事件、picker 与 widgets

import matplotlib.pyplot as plt
import numpy as np

fig, ax = plt.subplots()
sc = ax.scatter(np.random.default_rng(0).normal(size=200),
                np.random.default_rng(1).normal(size=200), s=40)

state = {'clicks': 0, 'last': None, 'zoom': 1.0}

def on_click(event):
    state['clicks'] += 1
    if event.inaxes is ax:
        state['last'] = (event.xdata, event.ydata)
        x, y = state['last']                       # 元组不能直接 :.3f 格式化
        print(f'click#{state["clicks"]} 数据坐标 ({x:.3f}, {y:.3f})')

def on_key(event):
    if event.key == 'z':
        state['zoom'] *= .8
        ax.set_xlim(-state['zoom'], state['zoom']); ax.set_ylim(-state['zoom'], state['zoom'])
        fig.canvas.draw_idle()
    elif event.key == 'r':
        ax.autoscale(); fig.canvas.draw_idle()

def n_cb():
    # ★ 别断言绝对数量：matplotlib 自己就挂了 4 个（缩放平移、图例、工具栏联动），
    #   所以刚画完的图上这里是 4，不是 0。
    return len(fig.canvas.callbacks.callbacks.get('button_press_event', {}))

print(n_cb())                                       # 输出: 4  ← 框架自带的
cid1 = fig.canvas.mpl_connect('button_press_event', on_click)
cid2 = fig.canvas.mpl_connect('key_press_event', on_key)
print(n_cb())                                       # 输出: 5
cid3 = fig.canvas.mpl_connect('button_press_event', on_key)   # 同一事件可注册多个
print(n_cb())                                       # 输出: 6
fig.canvas.mpl_disconnect(cid3)                     # 断开用返回的 cid，不是函数名
print(n_cb())                                       # 输出: 5

import matplotlib.pyplot as plt
import numpy as np

fig, ax = plt.subplots()
x = np.arange(10); y = x ** 2
sc = ax.scatter(x, y, s=60, picker=True)          # True = 命中半径 5 pt
line, = ax.plot(x, y, lw=3, picker=3)             # 数值 = 命中半径
bar = ax.bar(x, y, picker=True)

def on_pick(event):
    art = event.artist
    idx = event.ind if hasattr(event, 'ind') else None
    print(f'picked {type(art).__name__} idx={idx}')
    art.set_alpha(.4)                              # 高亮反馈

fig.canvas.mpl_connect('pick_event', on_pick)

import matplotlib.pyplot as plt
import numpy as np
from matplotlib.widgets import Slider, Button, RadioButtons, RangeSlider

fig, ax = plt.subplots(figsize=(6, 4))
x = np.linspace(0, 4*np.pi, 1000)
line, = ax.plot([], [], lw=1.5, color='C0')
ax.set(xlabel='t', ylabel='sin(k·t)')
lines = {'sin': np.sin, 'cos': np.cos, 'tan': np.tan}   # 名字 → 函数

ax_freq = fig.add_axes([.15, .12, .7, .03])
s_freq = Slider(ax_freq, '频率', 0.1, 10, valinit=1, valfmt='%.2f Hz')  # 3.11：valfmt 支持 callable

ax_amp = fig.add_axes([.15, .06, .7, .03])
s_amp = Slider(ax_amp, '振幅', 0, 3, valinit=1)
ax_band = fig.add_axes([.15, .89, .7, .03])
s_band = RangeSlider(ax_band, '频率区间', 0.1, 10, valinit=(0.5, 3))
ax_radio = fig.add_axes([.02, .2, .15, .15], facecolor='0.9')
radio = RadioButtons(ax_radio, list(lines), active=0,
                     activecolor='crimson', layout='vertical')   # 3.11 新增 layout
ax_btn = fig.add_axes([.78, .2, .12, .07])
btn = Button(ax_btn, '重置')

def update(val):
    amp = s_amp.val
    f = lines[radio.value_selected]        # value_selected 是字符串本身，不是列表
    y = amp * f(s_freq.val * x)
    line.set_data(x, y)                     # x 和 y 必须同时给全长度
    fig.canvas.draw_idle()

s_freq.on_changed(update); s_amp.on_changed(update); radio.on_clicked(update)
btn.on_clicked(lambda ev: (s_freq.reset(), s_amp.reset()))
update(s_freq.val)
plt.show()