title: Python re.compile. Unbalanced Parenthesis error
body: <p>I am trying to compile a regex to be able to accumulate a sequence of hashtags (<code>r'#\w+'</code>) from a tweet. I want to be able to compile two regexes which can do this from starting and end ing of the tweet. I am using python 272 and my code is like this. </p>
  
  <pre><code>HASHTAG_SEQ_REGEX_PATTERN           = r"""
  (                                       #Outermost grouping to match overall regex
  #\w+                                    #The hashtag matching. It's a valid combination of \w+
  ([:\s,]*#\w+)*                          #This is an optional (0 or more) sequence of hashtags separated by [\s,:]*
  )                                       #Closing parenthesis of outermost grouping to match overall regex
  """
  
  LEFT_HASHTAG_REGEX_SEQ      = re.compile('^' + HASHTAG_SEQ_REGEX_PATTERN , re.VERBOSE | re.IGNORECASE)
  </code></pre>
  
  <p>When the line where I'm compiling the regex is executed, I get following error:</p>
  
  <pre><code>sre_constants.error: unbalanced parenthesis
  </code></pre>
  
  <p>I don't know why am I getting this, as there is no unbalanced parenthesis that I can see in my Regex Pattern. </p>