|
|
|
|
.. Copyright (C) 2001-2020 NLTK Project
|
|
|
|
|
.. For license information, see LICENSE.TXT
|
|
|
|
|
|
|
|
|
|
===============================================
|
|
|
|
|
Generating sentences from context-free grammars
|
|
|
|
|
===============================================
|
|
|
|
|
|
|
|
|
|
An example grammar:
|
|
|
|
|
|
|
|
|
|
>>> from nltk.parse.generate import generate, demo_grammar
|
|
|
|
|
>>> from nltk import CFG
|
|
|
|
|
>>> grammar = CFG.fromstring(demo_grammar)
|
|
|
|
|
>>> print(grammar)
|
|
|
|
|
Grammar with 13 productions (start state = S)
|
|
|
|
|
S -> NP VP
|
|
|
|
|
NP -> Det N
|
|
|
|
|
PP -> P NP
|
|
|
|
|
VP -> 'slept'
|
|
|
|
|
VP -> 'saw' NP
|
|
|
|
|
VP -> 'walked' PP
|
|
|
|
|
Det -> 'the'
|
|
|
|
|
Det -> 'a'
|
|
|
|
|
N -> 'man'
|
|
|
|
|
N -> 'park'
|
|
|
|
|
N -> 'dog'
|
|
|
|
|
P -> 'in'
|
|
|
|
|
P -> 'with'
|
|
|
|
|
|
|
|
|
|
The first 10 generated sentences:
|
|
|
|
|
|
|
|
|
|
>>> for sentence in generate(grammar, n=10):
|
|
|
|
|
... print(' '.join(sentence))
|
|
|
|
|
the man slept
|
|
|
|
|
the man saw the man
|
|
|
|
|
the man saw the park
|
|
|
|
|
the man saw the dog
|
|
|
|
|
the man saw a man
|
|
|
|
|
the man saw a park
|
|
|
|
|
the man saw a dog
|
|
|
|
|
the man walked in the man
|
|
|
|
|
the man walked in the park
|
|
|
|
|
the man walked in the dog
|
|
|
|
|
|
|
|
|
|
All sentences of max depth 4:
|
|
|
|
|
|
|
|
|
|
>>> for sentence in generate(grammar, depth=4):
|
|
|
|
|
... print(' '.join(sentence))
|
|
|
|
|
the man slept
|
|
|
|
|
the park slept
|
|
|
|
|
the dog slept
|
|
|
|
|
a man slept
|
|
|
|
|
a park slept
|
|
|
|
|
a dog slept
|
|
|
|
|
|
|
|
|
|
The number of sentences of different max depths:
|
|
|
|
|
|
|
|
|
|
>>> len(list(generate(grammar, depth=3)))
|
|
|
|
|
0
|
|
|
|
|
>>> len(list(generate(grammar, depth=4)))
|
|
|
|
|
6
|
|
|
|
|
>>> len(list(generate(grammar, depth=5)))
|
|
|
|
|
42
|
|
|
|
|
>>> len(list(generate(grammar, depth=6)))
|
|
|
|
|
114
|
|
|
|
|
>>> len(list(generate(grammar)))
|
|
|
|
|
114
|
|
|
|
|
|
