Methods¶

cond¶

Reduce the boilerplate when choosing paths with DiverseFailableN. Think of this method as a functional if alternative for successful or failed types.

So, this code:

>>> from returns.result import Failure, Result, Success

>>> def is_numeric(string: str) -> Result[str, str]:
...     if string.isnumeric():
...          return Success('It is a number')
...     return Failure('It is not a number')

Can be replaced with this:

>>> from returns.methods import cond
>>> from returns.result import Failure, Result, Success

>>> def is_numeric(string: str) -> Result[str, str]:
...     return cond(
...         Result,
...         string.isnumeric(),
...         'It is a number',
...         'It is not a number',
...    )

>>> assert is_numeric('42') == Success('It is a number')
>>> assert is_numeric('text') == Failure('It is not a number')

Why is it helpful? Because cond can be easily added into a Pipelines of functions.

unwrap_or_failure¶

Unwraps either a successful or failed value.

>>> from returns.io import IO, IOSuccess, IOFailure
>>> from returns.methods import unwrap_or_failure

>>> assert unwrap_or_failure(IOSuccess(1)) == IO(1)
>>> assert unwrap_or_failure(IOFailure('a')) == IO('a')

Useful when you have a ResultLike value with correctly handled error value, for example with bimap(). Here’s a full example:

>>> from returns.result import Failure, Result, Success
>>> from returns.methods import unwrap_or_failure
>>> from returns.pointfree import bimap

>>> instance: Result[int, str] = Success(1)
>>> error_handled = bimap(lambda inr: inr + 1, lambda _: 0)(instance)
>>> assert isinstance(unwrap_or_failure(error_handled), int)

API Reference¶

cond(container_type, is_success, success_value, error_value=None)¶

Kinded version of internal_cond(), use it to infer real return type.

Parameters:

• container_type (Union[Type[TypeVar(_SingleFailableKind, bound= SingleFailableN)], Type[TypeVar(_DiverseFailableKind, bound= DiverseFailableN)]]) –

• is_success (bool) –

• success_value (TypeVar(_ValueType)) –

• error_value (Optional[TypeVar(_ErrorType)]) –

unwrap_or_failure(container)[source]¶

Unwraps either successful or failed value.

>>> from returns.io import IO, IOSuccess, IOFailure
>>> from returns.methods import unwrap_or_failure

>>> assert unwrap_or_failure(IOSuccess(1)) == IO(1)
>>> assert unwrap_or_failure(IOFailure('a')) == IO('a')

Parameters:

container (Unwrappable[TypeVar(_FirstType), TypeVar(_SecondType)]) –

Return type:

Union[TypeVar(_FirstType), TypeVar(_SecondType)]