regex.py

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"""
This module contains the RegexExtractor class, which is used to extract data using a regular expression.
"""
import re
import typing
from formatron.extractor import NonterminalExtractor
 
 
class RegexExtractor(NonterminalExtractor):
    """
    An extractor that extracts a string using a regular expression.
    """
 
    def __init__(self, regex: str, capture_name: str, nonterminal: str):
        """
        Initialize the regex extractor.
 
        Args:
            regex: The regular expression for extraction.
            capture_name: The name of the capture, or `None` if the extractor does not capture.
            nonterminal: The nonterminal representing the extractor.
        """
        super().__init__(nonterminal, capture_name)
        self._regex = re.compile(regex)
 
    def extract(self, input_str: str) -> typing.Optional[tuple[str, re.Match | None]]:
        """
        Extract the string using the regular expression.
        Specifically, the first match(if any) of the regex pattern in the input string is returned. 
 
        Args:
            input_str: The input string.
        Returns:
            The remaining string and the extracted `re.Match` object, or `None` if the extraction failed.
        """
        matched = self._regex.match(input_str)
        if not matched:
            return None
        return input_str[matched.span()[1]:], matched
 
    @property
    def kbnf_definition(self) -> str:
        return f"{self.nonterminal} ::= #{repr(self._regex.pattern)};"