Source Code for Module nltk.chunk.api

 1  # Natural Language Toolkit: Chunk parsing API 
 2  # 
 3  # Copyright (C) 2001-2011 NLTK Project 
 4  # Author: Edward Loper <edloper@gradient.cis.upenn.edu> 
 5  #         Steven Bird <sb@csse.unimelb.edu.au> (minor additions) 
 6  # URL: <http://www.nltk.org/> 
 7  # For license information, see LICENSE.TXT 
 8   
 9  ##////////////////////////////////////////////////////// 
10  ##  Chunk Parser Interface 
11  ##////////////////////////////////////////////////////// 
12   
13  from nltk.parse import ParserI 
14  import nltk 
15   
16 -class ChunkParserI(ParserI): 
17      """ 
18      A processing interface for identifying non-overlapping groups in 
19      unrestricted text.  Typically, chunk parsers are used to find base 
20      syntactic constituants, such as base noun phrases.  Unlike 
21      L{ParserI}, C{ChunkParserI} guarantees that the C{parse} method 
22      will always generate a parse. 
23      """ 
24 -    def parse(self, tokens): 
25          """ 
26          @return: the best chunk structure for the given tokens 
27          and return a tree. 
28           
29          @param tokens: The list of (word, tag) tokens to be chunked. 
30          @type tokens: C{list} of L{tuple} 
31          @rtype: L{Tree} 
32          """ 
33          assert 0, "ChunkParserI is an abstract interface" 
34   
35 -    def evaluate(self, gold): 
36          """ 
37          Score the accuracy of the chunker against the gold standard. 
38          Remove the chunking the gold standard text, rechunk it using 
39          the chunker, and return a L{ChunkScore<nltk.chunk.util.ChunkScore>} 
40          object reflecting the performance of this chunk peraser. 
41   
42          @type gold: C{list} of L{Tree} 
43          @param gold: The list of chunked sentences to score the chunker on. 
44          @rtype:  L{ChunkScore<nltk.chunk.util.ChunkScore>} 
45          """ 
46          chunkscore = nltk.chunk.util.ChunkScore() 
47          for correct in gold: 
48              chunkscore.score(correct, self.parse(correct.leaves())) 
49          return chunkscore 
50