title: NLTK-based text processing with pandas
body: <p>The punctuation and numerical,lowercase  are not working while using nltk.</p>
  
  <p><strong>My code</strong></p>
  
  <pre><code>stopwords=nltk.corpus.stopwords.words('english')+ list(string.punctuation)
  user_defined_stop_words=['st','rd','hong','kong']                    
  new_stop_words=stopwords+user_defined_stop_words
  
  def preprocess(text):
      return [word for word in word_tokenize(text) if word.lower() not in new_stop_words and not word.isdigit()]
  
  miss_data['Clean_addr'] = miss_data['Adj_Addr'].apply(preprocess)
  </code></pre>
  
  <p><strong>Sample Input</strong></p>
  
  <pre><code>23FLOOR 9 DES VOEUX RD WEST     HONG KONG
  PAG CONSULTING FLAT 15 AIA CENTRAL 1 CONNAUGHT RD CENTRAL
  C/O CITY LOST STUDIOS AND FLAT 4F 13-15 HILLIER ST SHEUNG HONG KONG
  </code></pre>
  
  <p><strong>Expected Output</strong></p>
  
  <pre><code> floor des voeux west
   pag consulting flat aia central connaught central
   co city lost studios flat f hillier sheung
  </code></pre>