title: python sklearn pipiline fit: "AttributeError: lower not found"
body: <p>I'm trying to classify sveveral text data into 3 categories using sklearn. But I'm getting </p>
  
  <blockquote>
    <p>"AttributeError: lower not found"</p>
  </blockquote>
  
  <p>when running.</p>
  
  <p><strong>Code:</strong></p>
  
  <pre><code>train, test = train_test_split(df, random_state=42, test_size=0.3, shuffle=True)
  X_train = train.contents
  X_test = test.contents
  Y_train = train.category
  Y_test = test.category
  
  clf_svc = Pipeline([('vect', CountVectorizer()),
                      ('tfidf', TfidfVectorizer(tokenizer=',', use_idf=True, stop_words="english")),
                      ('clf', OneVsRestClassifier(LinearSVC(), n_jobs=1)),
                      ])
  
  clf_svc = clf_svc.fit(X_train, Y_train)
  predicted_svc = clf_svc(X_test)
  print(np.mean(predicted_svc == Y_test))
  </code></pre>
  
  <p>Dataframe (df) consists of 2 columns: contents (long text data) and categories (text 
  data). contents are scraped texts thus contain tens or hundreds of words, and categories are single words such as "A", "B".</p>
  
  <p>I've already checked past questions in stackoverflow but I could not solve this error occuring.<br>
  I'd be very glad to know the solution, or problems in the code itself.<br>
  Any advice and answers will be greatly appreciated.</p>
  
  <p>Thanks in advance.</p>