API Reference¶
Currency¶
The currency module defines currencies of various types. Use them wherever you need to record loans or transactions of exchange.
Tallwallet 0.10.0 only defines a handful of currency types. Look out for improvements in future releases.
Finance¶
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class
tallywallet.common.finance.Note¶ Note(date, principal, currency, term, interest, period)
A Note keeps all the details of a promise to pay a debt, as follows:
- date
The date on which the loan is agreed.
- principal
The amount of the original loan.
- currency
The currency in which the loan will be paid.
- term
The duration of the loan.
- interest
The rate of interest.
- period
The period of time over which interest is calculated.
Create new instance of Note(date, principal, currency, term, interest, period)
The functions of the Finance module are all intended to be compatible with
the Note type. They either take
such an object as a parameter, or their keyword arguments can be supplied from
the result of the vars function on a
Note object.
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tallywallet.common.finance.value_simple(note: tallywallet.common.finance.Note)[source]¶ Returns the simple value of a promissory note on maturity.
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tallywallet.common.finance.value_series(date, principal, term, period, interest, m=1, **kwargs)[source]¶ Calculate the value of a debt over time. Parameters are as for the
Notetype. Additionally:- m
The number of times per period that interest is compounded.
This function is a generator. It produces 2-tuples of (date, value).
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tallywallet.common.finance.discount_simple(note: tallywallet.common.finance.Note)[source]¶ Calculates the discounted value of an ordinary simple annuity. See Schaum’s Mathematics of Finance Equation 5.2 .
Returns a 3-tuple of (number of payments, annualised rate, annuity payment)
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tallywallet.common.finance.schedule(note: tallywallet.common.finance.Note, places=2, rounding='ROUND_UP')[source]¶ Calculate the amortization schedule for a
Note.- places
An integer. Round the balance to this number of decimal places at each calculation interval.
- rounding
Selects the rounding method. Must be one of the constants defined for this purpose in the decimal standard library module.
This function is a generator. It produces a sequence of
Amortizationobjects.
-
class
tallywallet.common.finance.Amortization¶ Amortization(date, payment, interest, repaid, balance)
An Amortization object records a payment against an amortization schedule:
- date
The date on which the payment is made.
- payment
The total amount of the payment.
- interest
The amount paid as interest.
- repaid
The amount repaid from the principal.
- balance
The remaining balance of the loan.
Create new instance of Amortization(date, payment, interest, repaid, balance)
Trade¶
-
class
tallywallet.common.trade.TradePath¶ TradePath(rcv, work, out)
A 3-tuple of Currency objects, describing the path of a foreign exchange trade. The first element is the source currency, the second the reference currency of the account, and the third the destination currency.
Create new instance of TradePath(rcv, work, out)
-
class
tallywallet.common.trade.TradeGain¶ TradeGain(rcv, gain, out)
A 3-tuple of numerical values, describing the result of a change in foreign exchange rates. The first element is the value due to the prior rate, the second is the gain due to the rate change, and the third element is the final sum.
Create new instance of TradeGain(rcv, gain, out)
Exchange¶
The exchange module contains functionality to enable conversion between currencies.
-
class
tallywallet.common.exchange.Exchange¶ An exchange is a lookup container for currency exchange rates.
It behaves just like a Python dictionary, but has some extra methods.
The approach Tallywallet uses is to associate each rate against a key which is a 2-tuple of Currency. By convention, the first element of this key is the source currency, and the second is the destination. The values of the exchange mapping can therefore be considered as gain from one currency to the next.
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get(key)¶ Return the value stored against key.
This method overrides the standard behaviour of dict.get. It infers the values of missing keys as follows:
The rate of a currency against itself is unity.
The rate of one currency against another is the reciprocal of the reverse rate (if defined).
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convert(val, path, fees=TradeFees(rcv=0, out=0))¶ Return the calculated outcome of converting the amount val via the TradePath path.
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gain(val, path, prior=None, fees=TradeFees(rcv=0, out=0))¶ Calculate the gain related to a change in exchange rates. The self object contains the latest rates, and the historic ones are passed as an argument to this method.
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Ledger¶
The ledger module defines Ledger and some associated classes.
-
class
tallywallet.common.ledger.Role[source]¶ This enumeration contains definitions for the roles played by a column in a Ledger.
-
class
tallywallet.common.ledger.Column¶ Column(ref, currency, role, label)
A 4-tuple, describing a column in a Ledger.
Create new instance of Column(ref, currency, role, label)
-
class
tallywallet.common.ledger.Ledger(*args, ref=<Currency.XTW: 'tallywallet'>)[source]¶ This class implements the fundamental operations you need to perform Adjusted Cost Base accounting.
- Parameters
ref – (optional) the base Currency type for the Ledger
args – One or more Column objects
-
property
equation¶ The Fundamental Accounting Equation is this:
Assets - Liabilities = Capital + Income - Expenses - Dividends
Currency trading gains are counted as income. For practical purposes, the FAE is often rearranged to be:
Assets + Expenses + Dividends = Capital + Income + Liabilities
This property evaluates both sides of this second equation, and determines if they are equal or not.
- Returns
A tuple of lhs, rhs, status
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adjustments(exchange, cols=None)[source]¶ Calculates the effects of a change in exchange rates.
Supply an Exchange object and an optional sequence of columns. If no columns are specified then all are assumed.
The columns are recalculated (but not committed) against the new exchange rates.
This method will generate a sequence of 3-tuples; (TradeGain, Column, Exchange).
This output is compatible with the arguments accepted by the commit method.
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commit(trade, col, exchange=None, **kwargs)[source]¶ Applies a trade to the ledger.
If you supply an exchange argument, trade may be a TradeGain object. In this usage, a trading account in the currency of the ledger column will accept any exchange gain or loss.
Otherwise, trade should be a number. It will be added to the specified column in the ledger.
Output¶
Tallywallet has chosen RSON as the serialisation format for a Ledger. It’s a readable serial object notation which can be processed by text utilities or converted into Python objects.