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118 lines
3.7 KiB
Python
118 lines
3.7 KiB
Python
"""Multi strategy output parser."""
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import logging
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from abc import ABC, abstractmethod
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from typing import Any, Callable, Generic, Iterator, Sequence, TypeVar, Union, Optional
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from langchain.schema import (
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BaseOutputParser,
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OutputParserException,
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)
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log = logging.getLogger(__name__)
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T = TypeVar("T")
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S = TypeVar("S")
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TPredicate = Callable[[str], bool]
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TParser = Callable[[str], S]
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class ParseStrategy(Generic[S]):
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"""A strategy is a pair of (parser, predicate).
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This class behave like a tuple for easy definition of multiple strategies.
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"""
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def __init__(
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self, parser: TParser[S], predicate: TPredicate, name: Optional[str] = None
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):
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assert callable(parser), "first argument <parser> must be callable"
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self.parser = parser
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assert callable(predicate), "second argument <predicate> must be callable"
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self.predicate = predicate
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self.name = name
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def __repr__(self) -> str:
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if self.name is None:
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return f"ParseStrategy(parser={self.parser}," "predicate={self.predicate})"
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return (
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f"ParseStrategy[{self.name}](parser={self.parser},"
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"predicate={self.predicate})"
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)
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def __getitem__(self, index: int) -> Union[TParser[S], TPredicate]:
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"""Behaves like a tuple."""
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if index == 0:
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return self.parser
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elif index == 1:
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return self.predicate
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else:
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raise IndexError("tuple index out of range")
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def __iter__(self) -> Iterator[Any]:
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"""Implement tuple unpacking."""
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yield self.parser
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yield self.predicate
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class MultiStrategyParser(BaseOutputParser[T], ABC, Generic[T, S]):
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"""Try multiple strategies to parse the output.
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A strategy is a tuple of (parser, predicate). The parser takes the some
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text as input and returns some type S. The parser is only called if the
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predicate returns True.
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When the `parse` method is called, all registered strategies are tried
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in order and the first one that succeeds returns its result.
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The returned value of type `S` is then passed to the final_parse method to
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produce the final result compatible with the inhertited output parser
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interface.
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Appending a strategy to the end makes it a fallback strategy.
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"""
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class Config:
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arbitrary_types_allowed = True
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strategies: Sequence[ParseStrategy[S]]
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"""List of strategies to try. The first one that succeeds is returned."""
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def add_strategy(self, *strategy: ParseStrategy[S]) -> None:
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"""Register a new strategy.
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A strategy is a callbale that takes in text as `str` and returns
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some type `S`.
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"""
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self.strategies = [*self.strategies, *strategy]
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@abstractmethod
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def final_parse(self, text: str, parsed: S) -> T:
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"""Parse the output of a strategy."""
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def parse(self, text: str) -> T:
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"""Try the registered strategies in order.
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Returns the output of the first succeeding strategy."""
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if len(self.strategies) == 0:
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raise OutputParserException("No strategy available")
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for strategy, predicate in self.strategies:
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log.debug(f"trying strategy {strategy}")
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if not predicate(text):
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log.debug(f"Skipping strategy {strategy}")
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if predicate(text):
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try:
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parsed = strategy(text)
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result = self.final_parse(text, parsed)
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log.debug(f"Strategy {strategy} succeeded")
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return result
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except Exception:
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continue
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raise OutputParserException(f"Could not parse output: {text}")
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@property
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def _type(self) -> str:
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return "multi_strategy"
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