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PTA Standards

Commodity Validation ​

Overview ​

Commodity validation ensures currencies and commodities are used consistently, optionally requiring explicit declaration and enforcing account currency constraints.

Validation Rules ​

Currency Not Declared ​

Note: Python beancount 3.x does NOT require explicit commodity declarations. Currencies are implicitly recognized when used. The commodity directive is optional and primarily used for adding metadata.

Currency Constraint Violation ​

Postings MUST only use currencies allowed by the account's open directive. Violations produce a ValidationError.

Condition: Posting uses currency not in account's constraint list.

Example:

beancount
2024-01-01 open Assets:USDOnly USD

2024-01-15 * "Invalid currency"
  Assets:USDOnly   100 EUR    ; ValidationError: Account only allows USD
  Income:Gift

Fix:

beancount
; Option 1: Use allowed currency
2024-01-15 * "Valid"
  Assets:USDOnly   100 USD
  Income:Gift

; Option 2: Change account constraints
2024-01-01 open Assets:Multi USD,EUR

Currency Constraints ​

Open Directive Constraints ​

The open directive can specify allowed currencies:

beancount
; Only USD allowed
2024-01-01 open Assets:Checking USD

; Multiple currencies allowed
2024-01-01 open Assets:Brokerage USD,EUR,AAPL,MSFT

; Any currency allowed (no constraint)
2024-01-01 open Expenses:General

Constraint Checking ​

For each posting:

  1. Find the account's open directive
  2. If currencies are specified, verify posting currency is in the list
  3. If no currencies specified, any currency is allowed

Constraint Examples ​

beancount
2024-01-01 open Assets:Checking USD

; Valid - USD is allowed
2024-01-15 * "OK"
  Assets:Checking  100 USD
  Income:Salary

; Invalid - EUR not in constraint list
2024-01-15 * "Fail"
  Assets:Checking  100 EUR    ; ValidationError
  Income:Gift

; No constraint - anything allowed
2024-01-01 open Expenses:General

2024-01-15 * "OK"
  Expenses:General  50 JPY    ; OK - no constraint
  Assets:Cash

Operating Currency ​

The operating_currency option specifies the primary currency for reporting:

beancount
option "operating_currency" "USD"
option "operating_currency" "EUR"  ; Can have multiple

This option is additive—each declaration adds to the list. It affects reporting but does NOT enable any "strict mode" for commodity validation.

Commodity Declaration ​

Basic Declaration ​

beancount
2024-01-01 commodity USD
2024-01-01 commodity EUR
2024-01-01 commodity AAPL

With Metadata ​

beancount
2024-01-01 commodity AAPL
  name: "Apple Inc."
  asset-class: "stock"
  exchange: "NASDAQ"

Declaration Timing ​

Commodities should be declared before first use:

beancount
; Recommended order
2024-01-01 commodity USD
2024-01-01 commodity AAPL

2024-01-01 open Assets:Brokerage USD,AAPL

2024-01-15 * "Buy"
  Assets:Brokerage  10 AAPL {150 USD}
  Assets:Cash

Currency Naming ​

Format Rules ​

ebnf
currency = uppercase (currency_char)* uppercase_end?
uppercase = [A-Z]
currency_char = [A-Z0-9'._-]
uppercase_end = [A-Z0-9]
  • MUST start with uppercase letter (A-Z)
  • MUST end with uppercase letter or digit (A-Z, 0-9)

UNDEFINED: Whether there is a maximum currency name length is pending clarification. Tracked in: python-beancount.md conformance issues

Valid Names ​

USD
EUR
AAPL
VTSAX
BTC
AU
VTI.TO
BRK.B

Invalid Names ​

usd           ; Lowercase not allowed
$USD          ; Special character at start
USD-          ; Cannot end with special character

Common Validation Scenarios ​

Investment Account ​

beancount
2024-01-01 commodity USD
2024-01-01 commodity AAPL
2024-01-01 commodity MSFT

; Restrict to declared securities
2024-01-01 open Assets:Brokerage USD,AAPL,MSFT

2024-01-15 * "Buy Apple"
  Assets:Brokerage  10 AAPL {150 USD}    ; OK
  Assets:Brokerage  -1500 USD            ; OK

2024-01-16 * "Buy Google"
  Assets:Brokerage  5 GOOGL {140 USD}    ; ValidationError: GOOGL not allowed
  Assets:Brokerage  -700 USD

Multi-Currency Account ​

beancount
2024-01-01 open Assets:Travel USD,EUR,GBP

2024-03-15 * "ATM in Paris"
  Assets:Travel    200 EUR    ; OK
  Assets:Checking

2024-03-20 * "ATM in London"
  Assets:Travel    100 GBP    ; OK
  Assets:Checking

2024-03-25 * "ATM in Tokyo"
  Assets:Travel  10000 JPY    ; ValidationError: JPY not allowed
  Assets:Checking

Crypto Portfolio ​

beancount
2024-01-01 commodity USD
2024-01-01 commodity BTC
2024-01-01 commodity ETH
2024-01-01 commodity SOL

2024-01-01 open Assets:Crypto BTC,ETH,SOL
2024-01-01 open Assets:Fiat USD

2024-01-15 * "Buy"
  Assets:Crypto  0.5 BTC {42000 USD}
  Assets:Crypto  2 ETH {2500 USD}
  Assets:Fiat   -47000 USD

Note: Currency constraints are enforced per-account via the open directive, not via a global "strict" mode option.

Error Messages ​

Currency Constraint Error ​

ValidationError: Currency EUR is not allowed in account Assets:USDOnly
  allowed currencies: USD

Configuration Options ​

beancount
; Set operating currency(ies) for reporting
option "operating_currency" "USD"

Note: Options like "strict" and "infer_commodities" do not exist in Python beancount 3.x.

Implementation Notes ​

  1. Build set of declared commodities from commodity directives (optional, for metadata)
  2. Extract currency constraints from open directives
  3. For each posting, validate currency against account constraints
  4. Report constraint violations with account and allowed list