在python的學(xué)習(xí)過程中我看到一個模擬鳥群的例子，并可以用鼠標(biāo)左鍵創(chuàng)建一只新的鳥，用鼠標(biāo)右鍵驅(qū)散鳥群。在我運(yùn)行代碼的時候發(fā)現(xiàn)，點(diǎn)擊鼠標(biāo)左鍵和右鍵均沒有反應(yīng)。于是查閱資料，最后找到了問題所在，現(xiàn)在將解決問題的過程記錄下來，（如果只要結(jié)果的同學(xué)直接拉到最底下就可以了）

測試環(huán)境：
Win10，python3.6.4，matplotlib 2.1.2
測試代碼：
（代碼來源：《python極客項目編程》第五章）

import sys, argparse import math import numpy as np import matplotlib.pyplot as plt import matplotlib.animation as animation from scipy.spatial.distance import squareform, pdist, cdist from numpy.linalg import normwidth, height = 640, 480class Boids:"""class that represents Boids simulation"""def __init__(self, N):"""initialize the Boid simulation"""# initial position and velocitiesself.pos = [width/2.0, height/2.0] + 10*np.random.rand(2*N).reshape(N, 2)# normalized random velocitiesangles = 2*math.pi*np.random.rand(N)self.vel = np.array(list(zip(np.sin(angles), np.cos(angles))))self.N = N# minimum distance of approachself.minDist = 25.0# maximum magnitude of velocities calculated by "rules"self.maxRuleVel = 0.03# maximum magnitude of the final velocityself.maxVel = 2.0def tick(self, frameNum, pts, beak):"""Update the simulation by one time step."""# get pairwise distancesself.distMatrix = squareform(pdist(self.pos))# apply rules:self.vel += self.applyRules()self.limit(self.vel, self.maxVel)self.pos += self.velself.applyBC()# update datapts.set_data(self.pos.reshape(2*self.N)[::2],self.pos.reshape(2*self.N)[1::2])vec = self.pos + 10*self.vel/self.maxVelbeak.set_data(vec.reshape(2*self.N)[::2],vec.reshape(2*self.N)[1::2])def limitVec(self, vec, maxVel):"""limit the magnitide of the 2D vector"""mag = norm(vec)if mag > maxVel:vec[0], vec[1] = vec[0]*maxVel/mag, vec[1]*maxVel/magdef limit(self, X, maxVel):"""limit the magnitide of 2D vectors in array X to maxValue"""for vec in X:self.limitVec(vec, maxVel)def applyBC(self):"""apply boundary conditions"""deltaR = 2.0for coord in self.pos:if coord[0] > width + deltaR:coord[0] = -deltaRif coord[0] < - deltaR:coord[0] = width + deltaRif coord[1] > height + deltaR:coord[1] = - deltaRif coord[1] < - deltaR:coord[1] = height + deltaRdef applyRules(self):# apply rule #1: SeparationD = self.distMatrix < 25.0vel = self.pos * D.sum(axis=1).reshape(self.N, 1) - D.dot(self.pos)self.limit(vel, self.maxRuleVel)# distance threshold for alignment (different from separation)D = self.distMatrix < 50.0# apply rule #2: Alignmentvel2 = D.dot(self.vel)self.limit(vel2, self.maxRuleVel)vel += vel2# apply rule #3: Cohesionvel3 = D.dot(self.pos) - self.posself.limit(vel3, self.maxRuleVel)vel += vel3return veldef buttonPress(self, event):"""event handler for matplotlib button presses"""# print('run')# left-click to add a boidif event.button is 1:print('left button')self.pos = np.concatenate((self.pos, np.array([[event.xdata, event.ydata]])), axis=0)# generate a random velocityangles = 2*math.pi*np.random.rand(1)v = np.array(list(zip(np.sin(angles), np.cos(angles))))self.vel = np.concatenate((self.vel, v), axis=0)self.N += 1# right-click to scatter boidselif event.button is 3:print('right button')# add scattering velocityself.vel += 0.1*(self.pos - np.array([[event.xdata, event.ydata]]))def tick(frameNum, pts, beak, boids):# print frameNum"""update function for animation"""boids.tick(frameNum, pts, beak)return pts, beak# main() function def main():# use sys.argv if neededprint('starting boids...')parser = argparse.ArgumentParser(description="Implementing Craig Reynold's Boids...")# add argumentsparser.add_argument('--num-boids', dest='N', required=False)args = parser.parse_args()# set the initial number of boidsN = 100if args.N:N = int(args.N)# create boidsboids = Boids(N)# set up plotfig = plt.figure()ax = plt.axes(xlim=(0, width), ylim=(0, height))pts, = ax.plot([], [], markersize=10, c='k', marker='o', ls='None')beak, = ax.plot([], [], markersize=4, c='r', marker='o', ls='None')# add a "button press" event handlerfig.canvas.mpl_connect("button_press_event", boids.buttonPress)anim = animation.FuncAnimation(fig, tick, fargs=(pts, beak, boids), interval=50)plt.show()# call main if __name__ == '__main__':main()

正常運(yùn)行，但是點(diǎn)擊鼠標(biāo)無反應(yīng)。

思路：
首先，我想到的原因是matplotlib的UI交互部分可能已過時或已修改過。所以我谷歌了下matplotlib的UI交互功能實(shí)現(xiàn)。找到了這個網(wǎng)頁（http://www.guofei.site/2017/09/26/matplotlib3.html）
這個網(wǎng)頁寫的比較清楚，而且配有例子，所以我單獨(dú)新建一個文件測試這個網(wǎng)頁上的兩個例子。兩個例子都是可以正常運(yùn)行的。這就令我十分好奇，因為源代碼中需要判斷的是 event.button 這個變量，所以我就將例子做了下修改，只輸出 event.button 變量。結(jié)果如下
測試代碼：

import matplotlib.pyplot as plt import numpy as npfig, ax = plt.subplots() x = np.linspace(0, 10, 1000) y = np.sin(x) line = ax.plot(x, y)[0]def on_key_press(event):# print(event.name)print(event.button)print(type(event.button))print(event.button is 1)print(event.button == 1)fig.canvas.mpl_disconnect(fig.canvas.manager.key_press_handler_id) # 取消默認(rèn)快捷鍵的注冊 fig.canvas.mpl_connect('button_press_event', on_key_press) plt.show()

結(jié)果當(dāng)運(yùn)行代碼后，我點(diǎn)擊鼠標(biāo)左鍵，輸出卻是：

1 <class 'int'> False True

這時我突然想起之前看到的 is 和 == 是有區(qū)別的。 is 判斷的是前后兩個值的地址是否相同，而 == 判斷的才是前后兩個值是否相同，如下：

>>> a = 1 >>> b = 1.0 >>> a is b False >>> a == b True >>> id(a) 1356033504 >>> id(b) 1802191773368

所以只需要將源代碼中的 is 換為 == ，就可以創(chuàng)建和驅(qū)散鳥群了。

總結(jié)：
通過這個模擬鳥群的代碼，學(xué)習(xí)到了在python中用matplotlib實(shí)現(xiàn)UI交互功能及 is 和 == 的區(qū)別。

總結(jié)

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