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import re
from langchain_core.output_parsers import BaseOutputParser
class BooleanOutputParser(BaseOutputParser[bool]):
"""Parse the output of an LLM call to a boolean."""
true_val: str = "YES"
"""The string value that should be parsed as True."""
false_val: str = "NO"
"""The string value that should be parsed as False."""
def parse(self, text: str) -> bool:
"""Parse the output of an LLM call to a boolean.
Args:
text: output of a language model
Returns:
boolean
"""
regexp = rf"\b({self.true_val}|{self.false_val})\b"
truthy = {
val.upper()
for val in re.findall(regexp, text, flags=re.IGNORECASE | re.MULTILINE)
}
if self.true_val.upper() in truthy:
if self.false_val.upper() in truthy:
raise ValueError(
f"Ambiguous response. Both {self.true_val} and {self.false_val} "
f"in received: {text}."
)
return True
elif self.false_val.upper() in truthy:
if self.true_val.upper() in truthy:
raise ValueError(
f"Ambiguous response. Both {self.true_val} and {self.false_val} "
f"in received: {text}."
)
return False
raise ValueError(
f"BooleanOutputParser expected output value to include either "
f"{self.true_val} or {self.false_val}. Received {text}."
)
@property
def _type(self) -> str:
"""Snake-case string identifier for an output parser type."""
return "boolean_output_parser"
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