title: assign column names to the output of Series.str.extract()
body: <p>Im using </p>
  
  <pre><code>df[colname].str.extract(regex) 
  </code></pre>
  
  <p>to parse a column of strings into several columns. I'd like to be able to assign the column names at the same time, something like:</p>
  
  <pre><code>df[colname].str.extract(regex, columns=cnames) 
  </code></pre>
  
  <p>where:</p>
  
  <pre><code>cnames = ['col1','col2','col3']
  regex = r'(sometext\w)_(aa|bb)_(\d+-\d)'
  </code></pre>
  
  <p>Its possible with a clunky construction like:</p>
  
  <pre><code>df[colname].str.extract(regex).rename(columns = dict(zip(range(len(cnames)),cnames)))
  </code></pre>
  
  <p>Or else I could embed the column names in the regex as named groups, so the regex changes to:</p>
  
  <pre><code>regex = r'(?P&lt;col1&gt;sometext\w)_(?P&lt;col2&gt;aa|bb)_(?P&lt;col3&gt;\d+-\d)'
  </code></pre>
  
  <p>Am i missing something here, is there a simpler way?
  thanks</p>