Module Stemmer :: Class Stemmer

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# Class Stemmer

    object --+
             |
            Stemmer

An instance of a stemming algorithm.

The algorithm has internal state, so must not be called concurrently. ie, only a single thread should access the instance at any given time.

When creating a Stemmer object, there is one required argument: the name of the algorithm to use in the new stemmer. A list of the valid algorithm names may be obtained by calling the algorithms() function in this module. In addition, the appropriate stemming algorithm for a given language may be obtained by using the 2 or 3 letter ISO 639 language codes.

A second optional argument to the constructor for Stemmer is the size of cache to use. The cache implemented in this module is not terribly efficient, but benchmarks show that it approximately doubles performance for typical text processing operations, without too much memory overhead. The cache may be disabled by passing a size of 0. The default size (10000 words) is probably appropriate in most situations. In pathological cases (for example, when no word is presented to the stemming algorithm more than once, so the cache is useless), the cache can severely damage performance.

The "benchmark.py" script supplied with the PyStemmer distribution can be used to test the performance of the stemming algorithms with various cache sizes.

Instance Methods | [hide private]

__init__(...) Initialise a stemmer. |

a new object with type S, a subtype of T

__new__(T, S, ...) |

__purgeCache(...) |

stemWord(...) Stem a word. |

stemWords(...) Stem a list of words. |

Inherited from `object`: `__delattr__`, `__format__`, `__getattribute__`, `__hash__`, `__reduce__`, `__reduce_ex__`, `__repr__`, `__setattr__`, `__sizeof__`, `__str__`, `__subclasshook__`

Properties | [hide private]

| maxCacheSize Maximum number of entries to allow in the cache.
Inherited from `object`: `__class__`

Method Details | [hide private]

### __init__(...)
(Constructor)

Initialise a stemmer.

See the class documentation for details.

Overrides: object.__init__

### __new__(T, S, ...)

Returns: a new object with type S, a subtype of T
Overrides: object.__new__

### stemWord(...)

Stem a word.

This takes a single argument, `word`, which should either be a UTF-8 encoded string, or a unicode object.

The result is the stemmed form of the word. If the word supplied was a unicode object, the result will be a unicode object: if the word supplied was a string, the result will be a UTF-8 encoded string.

### stemWords(...)

Stem a list of words.

This takes a single argument, `words`, which must be a sequence, iterator, generator or similar.

The entries in `words` should either be UTF-8 encoded strings, or a unicode objects.

The result is a list of the stemmed forms of the words. If the word supplied was a unicode object, the stemmed form will be a unicode object: if the word supplied was a string, the stemmed form will be a UTF-8 encoded string.

Property Details | [hide private]

### maxCacheSize

Maximum number of entries to allow in the cache.

This may be set to zero to disable the cache entirely.

The maximum cache size may be set at any point - setting the maximum size will purge entries from the cache if the new maximum size is smaller than the current size.