title: Regex Difficulties Extracting Text for Pandas Dataframe
body: <p>I have run the regex code below on my data in an online regex tester and it works fine.  However, when I attempt to run it in Python 3 and Pandas 0.18 I get NaN in the new 'r' column.</p>
  
  <p>The regex codes is:</p>
  
  <pre><code>\(\(\d+,\s\d+\],\s\(\d+,\s(\d+)\]\)
  </code></pre>
  
  <p>Sample data is:</p>
  
  <pre><code>                   WT_g      r_25_text           r
  Azmuth_25   Range_25            
  (0, 5]      (0, 25]     1   ((0, 5],   (0, 25])     NaN
  (25, 30]    (25, 50]    1   ((25, 30], (25, 50])    NaN
  (35, 40]    (25, 50]    1   ((35, 40], (25, 50])    NaN
  (65, 70]    (50, 75]    1   ((65, 70], (50, 75])    NaN
  (85, 90]    (50, 75]    1   ((85, 90], (50, 75])    NaN
  (95, 100]   (25, 50]    1   ((95, 100], (25, 50])   NaN
  (100, 105]  (50, 75]    1   ((100, 105], (50, 75])  NaN
  (110, 115]  (50, 75]    1   ((110, 115], (50, 75])  NaN
  (115, 120]  (0, 25]     1   ((115, 120], (0, 25])   NaN
  </code></pre>
  
  <p>My code:</p>
  
  <pre><code>df_25_sum['r'] = df_25_sum['r_25_text'].str.extract('\(\(\d+,\s\d+\],\s\(\d+,\s(\d+)\]\)')
  df_25_sum
  </code></pre>
  
  <p>The output is the sample data above.  I get NaN when I add the new column based on an extract.</p>