docs: def vocab_freq(docs, limit=1e6, verbose=1, tokenizer=generate_tokens):
      """Get the set of words used anywhere in a sequence of documents and count occurrences
  
      >>> gen = ('label: ' + chr(ord('A') + i % 3)*3 for i in range(11))
      >>> vocab_freq(gen, verbose=0)
      Counter({'label': 11, 'AAA': 4, 'BBB': 4, 'CCC': 3})
      """
      total = Counter()
      try:
          limit = min(limit, docs.count())
          docs = docs.iterator()
      except:
          pass
      for i, doc in enumerate(docs):
          try:
              doc = doc.values()
          except AttributeError:
              if not isinstance(doc, basestring):
                  doc = ' '.join([stringify(v) for v in doc])
              else:
                  doc = stringify(doc)
          if i >= limit:
              break
          c = Counter(tokenizer(doc, strip=True, nonwords=False))
          if verbose and (verbose < 1e-3 or not i % int(limit * verbose)):
              print('{}: {} ... {}'.format(i, c.keys()[:3], c.keys()[-3:] if len(c.keys()) > 6 else ''))
          total += c
      return total