title: Pandas: strip numbers and parenthesis from string
body: <p>My pandas df:</p>
  
  <pre><code>df  = pd.DataFrame({'A':[1,2,3,4,5], 'B':['(AAAAA)2','(BCA)1','(CA)5','(DD)8','(ED)15']})
      A   B
  0   1   (AAAAA)2
  1   2   (BCA)1
  2   3   (CA)5
  3   4   (DD)8
  4   5   (ED)15
  </code></pre>
  
  <p>I want to strip parenthsis and numbers in the column <code>B</code> <br>
  Expected output is:</p>
  
  <pre><code>    A   B
  0   1   AAAAA
  1   2   BCA
  2   3   CA
  3   4   DD
  4   5   ED
  </code></pre>
  
  <p>So far I tried, </p>
  
  <pre><code>df['B'] = df['B'].str.extract('([ABCDE])')
  </code></pre>
  
  <p>But I only got:</p>
  
  <pre><code>    A   B
  0   1   A
  1   2   B
  2   3   C
  3   4   D
  4   5   E
  </code></pre>