nltk cant interpret grammar category PRP$ output by stanford parser

Question

I want to generate sentence from grammar retrived from stanford parser, but NLTK is not able to interpret PRP$.

from nltk.parse.stanford import StanfordParser
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Answer 1

ValueError: Unable to parse line 11: NP -> PRP$ NNS
Expected a nonterminal, found: $ NNS

I've no idea why you are trying to combine a hand-built CFG with the output of the Stanford parser, but here's a solution to this problem:

I quick inspection of nltk/grammar.py shows that $ is not a legal character for a non-terminal name. This can be easily corrected by patching the module like this:

import nltk
import re
nltk.grammar._STANDARD_NONTERM_RE = re.compile('( [\w/][\w$/^<>-]* ) \s*', re.VERBOSE)

In the above I just added $ to the regexp that you'll find in nltk/grammar.py. You can then create and use grammars that have $ in their productions:

grammar = nltk.grammar.CFG.fromstring("NP -> PRP$ NNS")