nltk.classify.apply_features(feature_func, toks, labeled=None)[source]

Use the LazyMap class to construct a lazy list-like object that is analogous to map(feature_func, toks). In particular, if labeled=False, then the returned list-like object’s values are equal to:

[feature_func(tok) for tok in toks]

If labeled=True, then the returned list-like object’s values are equal to:

[(feature_func(tok), label) for (tok, label) in toks]

The primary purpose of this function is to avoid the memory overhead involved in storing all the featuresets for every token in a corpus. Instead, these featuresets are constructed lazily, as-needed. The reduction in memory overhead can be especially significant when the underlying list of tokens is itself lazy (as is the case with many corpus readers).

  • feature_func – The function that will be applied to each token. It should return a featureset – i.e., a dict mapping feature names to feature values.
  • toks – The list of tokens to which feature_func should be applied. If labeled=True, then the list elements will be passed directly to feature_func(). If labeled=False, then the list elements should be tuples (tok,label), and tok will be passed to feature_func().
  • labeled – If true, then toks contains labeled tokens – i.e., tuples of the form (tok, label). (Default: auto-detect based on types.)