To identify LOCATION chunks, we can make a different kind of ChunkParserI subclass that uses the gazetteers corpus to identify location words. The gazetteers corpus is a WordListCorpusReader class that contains the following location words:
Country names
U.S. states and abbreviations
Major U.S. cities
Canadian provinces
Mexican states
The
LocationChunker class, found in chunkers.py, iterates over a tagged sentence looking for words that are found in the gazetteers corpus. When it finds one or more location words, it creates a LOCATION chunk using IOB tags. The helper method iob_locations() is where the IOB LOCATION tags are produced, and the parse() method converts these IOB tags into a Tree:
from nltk.chunk import ChunkParserI
from nltk.chunk.util import conlltags2tree
from nltk.corpus import gazetteers
class LocationChunker(ChunkParserI):
def __init__(self):
self.locations = set(gazetteers.words())
self.lookahead = 0
for loc in self.locations...