Source code for cfpq_data.grammars.readwrite.cnf
"""Read (and write) a context-free grammar in Chomsky normal form
from (and to) different sources."""
import logging
import pathlib
from typing import Union
from pyformlang.cfg import Variable, CFG
from cfpq_data.grammars.converters.cnf import cnf_from_cfg
from cfpq_data.grammars.readwrite.cfg import cfg_from_text
__all__ = [
"cnf_from_text",
"cnf_from_txt",
]
[docs]
def cnf_from_text(text: str, *, start_symbol: Variable = Variable("S")) -> CFG:
"""Create a context-free grammar in Chomsky normal form [1]_ from text.
Parameters
----------
text : str
The text with which the context-free grammar in Chomsky normal form
will be created.
start_symbol : Variable
Start symbol of a context-free grammar.
Examples
--------
>>> from cfpq_data import *
>>> cnf = cnf_from_text("S -> a b")
>>> cfg_to_text(cnf)
'S -> a#CNF# b#CNF#\\na#CNF# -> a\\nb#CNF# -> b'
Returns
-------
cnf : CFG
Context-free grammar in Chomsky normal form.
References
----------
.. [1] https://en.wikipedia.org/wiki/Chomsky_normal_form
"""
cnf = cnf_from_cfg(cfg_from_text(text, start_symbol=start_symbol))
logging.info(f"Create {cnf=} from {text=}, {start_symbol=}")
return cnf
[docs]
def cnf_from_txt(
path: Union[pathlib.Path, str], *, start_symbol: Variable = Variable("S")
) -> CFG:
"""Create a context-free grammar in Chomsky normal form [1]_ from TXT file.
Parameters
----------
path : Union[Path, str]
The path to the TXT file with which the context-free grammar
in Chomsky normal form will be created.
start_symbol : Variable
Start symbol of a context-free grammar.
Examples
--------
>>> from cfpq_data import *
>>> cnf_1 = cfg_from_text("S -> a b")
>>> path = cfg_to_txt(cnf_1, "test.txt")
>>> cnf = cnf_from_txt(path)
>>> cfg_to_text(cnf)
'S -> a#CNF# b#CNF#\\na#CNF# -> a\\nb#CNF# -> b'
Returns
-------
cnf : CFG
Context-free grammar in Chomsky normal form.
References
----------
.. [1] https://en.wikipedia.org/wiki/Chomsky_normal_form
"""
with open(path, "r") as f:
productions = f.read()
cnf = cnf_from_text(productions, start_symbol=start_symbol)
logging.info(f"Create {cnf=} from {path=}, {start_symbol=}")
return cnf
