问题：

module'matplotlib.mlab'has no attribute 'normpdf'

原因：

mlab中normpdf属性已经移除了，报错信息：

module 'matplotlib.mlab' has no attribute 'normpdf'

解决方法：

加入from scipy.stats import norm

使用norm.pdf 替代normpdf

源代码：

import numpy as np
import matplotlib.mlab as mlab
import matplotlib.pyplot as plt
 
def demo2():
  mu, sigma , num_bins = 0, 1, 50
  x = mu + sigma * np.random.randn(1000000)
  # 正态分布的数据
  n, bins, patches = plt.hist(x, num_bins, normed=True, facecolor = 'blue', alpha = 0.5)
  # 拟合曲线
  y = norm.pdf(bins, mu, sigma)
  plt.plot(bins, y, 'r--')
  plt.xlabel('Expectation')
  plt.ylabel('Probability')
  plt.title('histogram of normal distribution: $\mu = 0$, $\sigma=1$')
 
  plt.subplots_adjust(left = 0.15)
  plt.show()
 
demo2()

修改：

# -*- coding: utf-8 -*-
"""
Created on Fri Apr  2 12:53:50 2021
@author: zhangjie
"""
 
import numpy as np
import matplotlib.mlab as mlab
import matplotlib.pyplot as plt
from scipy.stats import norm
 
def demo2():
  mu, sigma , num_bins = 0, 1, 50
  x = mu + sigma * np.random.randn(1000000)
  # 正态分布的数据
  n, bins, patches = plt.hist(x, num_bins, normed=True, facecolor = 'blue', alpha = 0.5)
  # 拟合曲线
  y = norm.pdf(bins, mu, sigma)
  plt.plot(bins, y, 'r--')
  plt.xlabel('Expectation')
  plt.ylabel('Probability')
  plt.title('histogram of normal distribution: $\mu = 0$, $\sigma=1$')
 
  plt.subplots_adjust(left = 0.15)
  plt.show()
 
demo2()