'Apply all feature extractor functions to the documents. This is a wrapper
around `nltk.classify.util.apply_features`.
If `labeled=False`, return featuresets as:
[feature_func(doc) for doc in documents]
If `labeled=True`, return featuresets as:
[(feature_func(tok), label) for (tok, label) in toks]
:param documents: a list of documents. `If labeled=True`, the method expects
a list of (words, label) tuples.
:rtype: LazyMap'

def apply_features(self, documents, labeled=None):

    return apply_features(self.extract_features, documents, labeled)
