Contracts

A contract is the configuration object you pass alongside your text to paxman.canonicalize(). It answers three questions: which capability to use, which patterns should count, and how the answer should look. Every capability provides the same contract surface so you only learn it once.

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What a contract is

You never construct a contract by hand. Each capability exposes a typed factory:

from paxman.capabilities import Email, Country

email_contract = Email.create_contract()
country_contract = Country.create_contract(include_localized=True)

The returned object is a frozen dataclass — you can inspect it, but not mutate it. Pass it straight to canonicalize():

result = paxman.canonicalize("Alemania", country_contract)

The contract’s capability_name field (set automatically) is how the engine selects the matching capability — see Capabilities.

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The unanimous surface

Every contract — no matter the capability — carries the same common fields. This is intentional: the shape is homogeneous so tooling, notebooks, and future capabilities all behave the same way.

Field	Type	Default	What it does
capability_name	str	set by factory	Which capability this contract selects. You never set it — the factory does.
excluded_rules	tuple[str, ...]	()	Rule names to skip during validation.
pinned_rules	tuple[str, ...] | None	None	If set, only these rules run (overrides excluded_rules). () pins to nothing.
year	int | None	None	Temporal filter — only rules published in or before this year run.
output_format	str | None	None → default	How the canonical value is rendered (see below).
extra_grammars	tuple[str, ...]	()	Community grammar names to opt in (advanced — see extending docs in a later round).

Precedence: when pinned_rules is non-None it wins over excluded_rules; year is applied after either pinning or exclusion.

output_format — always optional

output_format is the only presentation knob and it is always optional:

• None, "default", and the capability’s DEFAULT_OUTPUT_FORMAT all resolve to the default rendering.
• Any value in OFFERED_OUTPUT_FORMATS resolves to itself (e.g. "hyphenated" for ISBN, "rfc3966" for Phone).
• Anything else raises ContractError.

Validation of the canonical value is never affected by output_format — formatting happens after validation.

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Per-capability flags

Beyond the common fields, each contract adds flags that make sense for its domain. You will discover them through the factory’s signature and your editor’s autocomplete; the table below summarizes the current release.

Capability	Flag	Type	Default	Meaning
Email	include_obfuscated	bool	False	Recognize user at domain dot com style addresses
Email	include_localhost	bool	True	Recognize admin@localhost
Country	include_localized	bool	False	Recognize CLDR multilingual names (e.g. Alemania → DE)
Country	include_historical	bool	False	Recognize deprecated/historical names (e.g. Burma → BU)
IP	include_ipv6	bool	True	Recognize IPv6 addresses
ISBN	include_isbn10	bool	True	Recognize legacy ISBN-10
ISBN	include_range_validation	bool	False	Enable registrant-range provenance
Currency	default_currency	str | None	None	Resolve shared bare symbols ($) to this code when it is one of that symbol’s candidates
Money	dollar_sign_currency	str | None	None	Resolve bare $ amounts to this code
Money	precision	str	"strict"	Over-precision handling: strict / truncate / round
Phone	default_country	str | None	None	Resolve national numbers as if dialed in this country ("US")
SI Unit	allow_split_word_prefixes	bool	False	Merge kilo gram → kg
SI Unit	allow_multi_solidus	bool	False	Preserve kg/m/s instead of rejecting it
Date	two_digit_base_year	int | None	None	Base year for 2-digit year expansion
Date / ISBN / Phone / …	output_format	str	capability default	See capability-specific offered formats

This table reflects the current release. As new capabilities are added, each will document its own flags in the same way — the common fields above stay the same.

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How flags map to the pipeline

A useful mental model: the two groups of flags gate the two groups of pipeline stages (see Pipeline).

• Input-shape flags (include_*) toggle grammars — a disabled grammar simply never sees the input, so the status becomes MISSING rather than INVALID.
• Authority flags (requires_features on rules, plus excluded_rules/pinned_rules/year) gate rules — a dropped rule means the match was recognized but not accepted, so the status becomes INVALID.

You never branch inside a rule’s logic based on include_* — the flag’s presence or absence decides whether the rule runs at all.

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Common recipes

Narrow to specific specs

from paxman.capabilities import Email

# Only RFC 5322, no localhost
contract = Email.create_contract(pinned_rules=["Section 3.4.1-addr-spec"])

Exclude one spec

contract = Email.create_contract(excluded_rules=["Section 6.3-localhost"])

Time-travel to an older spec set

from paxman.capabilities import Date

contract = Date.create_contract(year=2019)  # only rules published ≤ 2019

Choose a rendering

from paxman.capabilities import Phone, ISBN

Phone.create_contract(output_format="rfc3966")  # tel:+15551234567
ISBN.create_contract(output_format="hyphenated")  # 978-0-11-000222-4
Phone.create_contract(output_format="national")  # national form
ISBN.create_contract(output_format="isbn13")  # bare digits (default)
# None / "default" also resolve to the default for any capability

Any non-offered value raises ContractError — you get a fast, typed failure instead of a silently wrong rendering.

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In plain language

Think of a contract as a work order you hand to a department. It says: here is the kind of job (capability), here are the tools you may use (which grammars and rules), and here is how I want the answer formatted (output_format). The department may have extra switches that only make sense for its work (e.g. Country’s “also accept historical names”), but the top of the form — excluded/pinned rules, year, output format — looks the same in every department.

Next: Pipeline → — what Paxman does with that work order.