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from typing import Callable, Union, Any, TypeVar, Type
from discord.ext.commands import Converter, UserInputError
from discord.utils import maybe_coroutine
C = TypeVar('C', bound=Converter)
class AugmentedConverter(Converter):
"""
Augment an existing converter by mapping its result or filtering based on its output.
Mapping is applied before filtering.
"""
async def convert(self, ctx, argument):
converter = self.original_converter
if issubclass(converter, Converter):
converter = converter()
if isinstance(converter, Converter):
converter = converter.convert
result = await converter(ctx, argument)
if await maybe_coroutine(self.filter_function, result):
return result
raise UserInputError()
def __init__(self, original_converter: Union[C, Type[C], Callable], mapping_function: Callable[[Any], Any] = None,
filter_function: Callable[[Any], bool] = None, error_message: str = None):
"""
:param original_converter: the converter augment. can be a function, converter or converter class. must be async
:param mapping_function: maps the result of the converter before any filtering takes place. optional
:param filter_function: filters the result. if this function returns a falsey value an `UserInputError` is
risen and then caught by discord.ext.commands
:param error_message: the error message that is thrown. this can be accessed by a custom error handler
"""
self.original_converter = original_converter
self.mapping_function = mapping_function or (lambda x: x)
self.filter_function = filter_function or (lambda _: True)
self.error_message = error_message
def non_nullable(converter: Union[C, Type[C], Callable], error_message: str = None):
"""
augments a converter to raise a UserInputError when None is returned. Useful for Greedy or Optional matchers.
:param converter: the converter to augment
:param error_message: the error message to be associated with the UserInputError
:return: the augmented converter
"""
return AugmentedConverter(converter, filter_function=lambda res: res is not None, error_message=error_message)
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