title: Although tables have already been installed on my pc, error appears every time when I run the code below
body: <pre><code>import pandas as pd
  import numpy as np
  import matplotlib.pyplot as plt
  plt.close('all')
  ts=pd.Series(np.random.randn(1000),index=pd.date_range('1/1/2020',periods=1000))
  ts=ts.cumsum()
  ts.plot()
  df=pd.DataFrame(np.random.randn(1000,4),index=ts.index,columns=['A','B','C','D'])
  df=df.cumsum()
  plt.figure()
  df.plot()
  plt.legend(loc='best')
  df.to_hdf('foo.h5', 'df')
  </code></pre>
  <h2><strong>Error message:</strong></h2>
  <p>ImportError: Missing optional dependency 'tables'.  Use pip or conda to install tables.</p>
  <p><strong>That is the cmd command:</strong></p>
  <p>C:\Users\rehim&gt;pip install --user tables</p>
  <p><strong>The result:</strong></p>
  <p>Requirement already satisfied: tables in c:\users\rehim\appdata\roaming\python\python38\site-packages (3.6.1)
  Requirement already satisfied: numpy&gt;=1.9.3 in c:\users\rehim\appdata\local\programs\python\python38\lib\site-packages (from tables) (1.19.2)
  Requirement already satisfied: numexpr&gt;=2.6.2 in c:\users\rehim\appdata\roaming\python\python38\site-packages (from tables) (2.7.1)</p>