fixfield

Fixed-decimal arithmetic for Python with per-field precision enforcement.

Inspired by COBOL's PIC clause — declare precision once on the field and it is enforced automatically on every assignment and arithmetic result.

pip install fixfield   # or: uv add fixfield

Requires Python 3.14+

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Quick start

from fixfield import Record, CurrencyField, ExternalField
import uuid

class Invoice(Record):
    invoice_id = ExternalField(uuid.UUID, default_factory=uuid.uuid4,
                               json_encoder=str, json_decoder=uuid.UUID)
    price      = CurrencyField()
    tax        = CurrencyField()
    total      = CurrencyField()

inv = Invoice(price="19.99", tax="0.00")
inv.tax   = inv.price * "0.0825"   # → 1.65
inv.total = inv.price + inv.tax    # → 21.64

print(repr(inv))
# Invoice(invoice_id=UUID('...'), price=19.99, tax=1.65, total=21.64)

print(inv.to_json())
# {"invoice_id": "...", "price": "19.99", "tax": "1.65", "total": "21.64"}

restored = Invoice.from_json(inv.to_json())
assert restored == inv

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Documentation

📖 User Guide — concepts, all field types, serialisation
🔎 API Reference — every class and parameter
📋 Changelog

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Why not just use decimal.Decimal?

	decimal.Decimal	fixfield
Precision location	Global context or per .quantize()	Declared on the field, enforced automatically
Per-field rounding	Manual on every result	Declarative
Overflow protection	None	digits cap + FieldOverflowError
Domain modelling	Plain values	Named record schema
Non-decimal fields	Anything	ExternalField[T]
Legacy serialisation	Manual	to_string / from_string

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License

MIT