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graflo.architecture.refusal

The base class every merge-time refusal shares.

A refusal carries two structured fields beside its prose. check names the rule that refused -- the parenthesised phrase the message already spells out -- and subjects the names it is about, as :func:~graflo.architecture.evolution.equivalence.subject ids such as left:Firm or left:Firm.firm_id. Both are optional and neither appears in the message, so a caller that only reads str(exc) sees exactly what it saw before they existed.

The two fields are what lets a caller classify a refusal without parsing its prose: :mod:graflo.architecture.evolution.preview keys its finding kinds on check, and a refusal that carries none is one the preview is not asked to anticipate.

This module sits at the bottom of the import order deliberately. The schema layer raises refusals of its own, so the base cannot live beside the merge machinery that consumes them.

Classes

Refusal

Bases: ValueError

A declaration that a combining operation will not carry out.

Subclasses name the layer that refused -- the cluster resolver, the canonical map, the schema union, the field fold. Deriving from :class:ValueError rather than replacing it keeps every existing except ValueError and pytest.raises(ValueError) working, which is what makes adding the structured fields a non-breaking change.

Source code in graflo/architecture/refusal.py 
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class Refusal(ValueError):
    """A declaration that a combining operation will not carry out.

    Subclasses name the layer that refused -- the cluster resolver, the
    canonical map, the schema union, the field fold. Deriving from
    :class:`ValueError` rather than replacing it keeps every existing
    ``except ValueError`` and ``pytest.raises(ValueError)`` working, which is
    what makes adding the structured fields a non-breaking change.
    """

    def __init__(
        self, message: str, *, check: str = "", subjects: tuple[str, ...] = ()
    ) -> None:
        super().__init__(message)
        self.check = check
        self.subjects = subjects

Attributes

check = check instance-attribute
subjects = subjects instance-attribute

Methods:

__init__(message, *, check='', subjects=())
Source code in graflo/architecture/refusal.py 
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def __init__(
    self, message: str, *, check: str = "", subjects: tuple[str, ...] = ()
) -> None:
    super().__init__(message)
    self.check = check
    self.subjects = subjects