historical: Add a setting to denominate Ledger conversions.

This makes conversion output easier to add to ledgers directly.

oxrlib/commands/historical.py

@@ -55,14 +55,16 @@ class Formatter:
 
 
 class LedgerFormatter(Formatter):
-    RATE_PREC = 5
+    def __init__(self, rate, signed_currencies=(), base_fmt='#,##0.###',
+                 rate_precision=5, denomination=None):
+        super().__init__(rate, signed_currencies, base_fmt)
+        self.rate_prec = rate_precision
+        self.denomination = denomination
 
-    def normalize_rate(self, rate, prec=None):
+    def normalize_rate(self, rate):
-        # Return prec nonzero digits of precision, if available.
-        if prec is None:
-            prec = self.RATE_PREC
         _, digits, exponent = rate.normalize().as_tuple()
-        prec -= min(0, exponent + len(digits))
+        # Return ``self.rate_prec`` nonzero digits of precision, if available.
+        prec = self.rate_prec - min(0, exponent + len(digits))
         quant_to = '1.{}'.format('0' * prec)
         try:
             qrate = rate.quantize(decimal.Decimal(quant_to))
@@ -71,11 +73,11 @@ class LedgerFormatter(Formatter):
             qrate = rate
         return qrate.normalize()
 
-    def format_rate(self, rate, prec=None):
+    def format_rate(self, rate):
-        return str(self.normalize_rate(rate, prec))
+        return str(self.normalize_rate(rate))
 
-    def format_ledger_rate(self, rate, curr, prec=None):
+    def format_ledger_rate(self, rate, curr):
-        nrate = self.normalize_rate(rate, prec)
+        nrate = self.normalize_rate(rate)
         rate_s = self.format_currency(nrate, curr, currency_digits=False)
         return "{{={0}}} @ {0}".format(rate_s)
 
@@ -85,13 +87,28 @@ class LedgerFormatter(Formatter):
         return "{} {} {}".format(
             from_amt, from_curr, self.format_ledger_rate(to_amt, to_curr))
 
+    def _denomination_for(self, currency, default):
+        if self.denomination is None:
+            return default
+        elif self.denomination == currency:
+            return None
+        else:
+            return self.denomination
+
+    def format_denominated_rate(self, amount, currency, default_denomination):
+        denomination = self._denomination_for(currency, default_denomination)
+        amt_s = self.format_currency(amount, currency)
+        if denomination is None:
+            return amt_s
+        else:
+            rate = self.rate.convert(1, currency, denomination)
+            return "{} {}".format(amt_s, self.format_ledger_rate(rate, denomination))
+
     def format_conversion(self, from_amt, from_curr, to_curr):
-        to_rate = self.rate.convert(1, from_curr, to_curr)
         to_amt = self.rate.convert(from_amt, from_curr, to_curr)
-        return "{} {}\n{}".format(
+        return "{}\n{}".format(
-            self.format_currency(from_amt, from_curr),
+            self.format_denominated_rate(from_amt, from_curr, to_curr),
-            self.format_ledger_rate(to_rate, to_curr),
+            self.format_denominated_rate(to_amt, to_curr, None),
-            self.format_currency(to_amt, to_curr),
         )
 
 
@@ -102,7 +119,8 @@ def run(config, stdout, stderr):
     if loaders.should_cache():
         config.cache.save_rate(rate)
     if config.args.ledger:
-        formatter = LedgerFormatter(rate, config.args.signed_currencies)
+        formatter = LedgerFormatter(rate, config.args.signed_currencies,
+                                    denomination=config.args.denomination)
     else:
         formatter = Formatter(rate)
     if not config.args.from_currency:

oxrlib/config.py

@@ -20,6 +20,7 @@ def currency_list(s):
 class Configuration:
     DATE_SEPS = frozenset('.-/ ')
     DEFAULT_CONFIG_PATH = pathlib.Path(HOME_PATH, '.config', 'oxrlib.ini')
+    NO_DENOMINATION = object()
     PREPOSITIONS = frozenset(['in', 'to', 'into'])
     TODAY = datetime.date.today()
 
@@ -97,6 +98,17 @@ class Configuration:
             action='store_false', dest='ledger',
             help="Turn off an earlier --ledger setting",
         )
+        hist_parser.add_argument(
+            '--denomination',
+            metavar='CODE', type=currency_code,
+            help="In Ledger conversion output, always show rates to convert "
+            "to this currency",
+        )
+        hist_parser.add_argument(
+            '--no-denomination',
+            dest='denomination', action='store_const', const=self.NO_DENOMINATION,
+            help="Turn off an earlier --denomination setting",
+        )
         hist_parser.add_argument(
             '--signed-currency', '--sign-currency',
             type=currency_code, action='append', dest='signed_currencies',
@@ -132,14 +144,16 @@ class Configuration:
         return configparser.ConfigParser()
 
     def _read_from_conffile(self, argname, sectionname, fallback, convert_to=None,
-                            confname=None, getter='get', unset=None):
+                            confname=None, getter='get', unset=None,
+                            *, convert_fallback=False):
         if getattr(self.args, argname) is not unset:
             return
         elif confname is None:
             confname = argname
         get_method = getattr(self.conffile, getter)
         value = get_method(sectionname, confname, fallback=fallback)
-        if convert_to is not None:
+        if (convert_to is not None
+            and (value is not fallback or convert_fallback)):
             value = self._convert_or_error(convert_to, value, confname)
         setattr(self.args, argname, value)
 
@@ -162,7 +176,12 @@ class Configuration:
             # Don't let the user specify ambiguous dates.
             self.error("historical data not available from year {}".format(year))
         self._read_from_conffile('base', 'Historical', 'USD', currency_code)
-        self._read_from_conffile('signed_currencies', 'Historical', self.args.base, currency_list)
+        if self.args.denomination is self.NO_DENOMINATION:
+            self.args.denomination = None
+        else:
+            self._read_from_conffile('denomination', 'Historical', None, currency_code)
+        self._read_from_conffile('signed_currencies', 'Historical', self.args.base,
+                                 currency_list, convert_fallback=True)
         self._read_from_conffile('ledger', 'Historical', False, getter='getboolean')
         self.args.to_currency = self.args.base
         if self.args.word4 and (self.args.word3.lower() in self.PREPOSITIONS):

oxrlib_example.ini

@@ -27,6 +27,13 @@ base = USD
 # Write output in Ledger format.
 ledger = no
 
+# Denominate Ledger books in this currency.
+# Ledger-formatted conversions will always show a rate to convert to this
+# currency, even when converting between two other currencies.
+# If not specified, output will show the rate for the currency you're
+# converting to.
+denomination = USD
+
 # Use signs for these currencies in Ledger output.
 # If not specified, defaults to the base currency.
 signed_currencies = USD, EUR

setup.py

@@ -5,7 +5,7 @@ from setuptools import setup
 setup(
     name='oxrlib',
     description="Library to query the Open Exchange Rates (OXR) API",
-    version='1.3',
+    version='1.4',
     author='Brett Smith',
     author_email='brettcsmith@brettcsmith.org',
     license='GNU AGPLv3+',

tests/test_historical.py

@@ -49,6 +49,7 @@ def build_config(
         to_currency=None,
         ledger=False,
         signed_currencies=None,
+        denomination=None,
         base='USD',
 ):
     return FakeConfig(responder, {
@@ -59,6 +60,7 @@ def build_config(
         'to_currency': base if to_currency is None else to_currency,
         'ledger': ledger,
         'signed_currencies': [base] if signed_currencies is None else signed_currencies,
+        'denomination': denomination,
     })
 
 def lines_from_run(config, output):
@@ -117,3 +119,30 @@ def test_signed_currencies(historical1_responder, output):
     assert next(lines) == '1 AED {=0.2723 USD} @ 0.2723 USD\n'
     assert next(lines) == '1 USD {=3.67246 AED} @ 3.67246 AED\n'
     assert next(lines, None) is None
+
+def test_denomination(historical1_responder, output):
+    config = build_config(historical1_responder, from_currency='ANG',
+                          to_currency='AED', amount=10,
+                          ledger=True, denomination='USD')
+    lines = lines_from_run(config, output)
+    assert next(lines) == '10.00 ANG {=$0.55866} @ $0.55866\n'
+    assert next(lines) == '20.52 AED {=$0.2723} @ $0.2723\n'
+    assert next(lines, None) is None
+
+def test_redundant_denomination(historical1_responder, output):
+    config = build_config(historical1_responder, from_currency='ANG',
+                          to_currency='USD', amount=10,
+                          ledger=True, denomination='USD')
+    lines = lines_from_run(config, output)
+    assert next(lines) == '10.00 ANG {=$0.55866} @ $0.55866\n'
+    assert next(lines) == '$5.59\n'
+    assert next(lines, None) is None
+
+def test_from_denomination(historical1_responder, output):
+    config = build_config(historical1_responder, from_currency='USD',
+                          to_currency='ALL', amount=10,
+                          ledger=True, denomination='USD')
+    lines = lines_from_run(config, output)
+    assert next(lines) == '$10.00\n'
+    assert next(lines) == '1,445 ALL {=$0.006919} @ $0.006919\n'
+    assert next(lines, None) is None