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23dfb3f899
A pure, offline regex check (no network) so a frozen value object stays pure. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
26 lines
921 B
Python
26 lines
921 B
Python
from __future__ import annotations
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import re
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from dataclasses import dataclass
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# UK postcode format, matched against the canonical (no-space, upper) value.
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# A pure structural check — it does not confirm the postcode actually exists
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# (that would need a network lookup, which a value object must not do).
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_UK_POSTCODE_RE = re.compile(r"[A-Z]{1,2}\d[A-Z\d]?\d[A-Z]{2}")
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@dataclass(frozen=True)
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class Postcode:
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value: str
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def __post_init__(self) -> None:
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# Frozen dataclass: bypass the descriptor with object.__setattr__.
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object.__setattr__(self, "value", "".join(self.value.split()).upper())
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def __str__(self) -> str:
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return self.value
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def is_valid(self) -> bool:
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"""Whether the canonical value is a well-formed UK postcode (format
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only — no existence check, so it is pure and offline)."""
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return _UK_POSTCODE_RE.fullmatch(self.value) is not None
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