historical: Normalize class instantiation for formatters.

This will make them easier to extend with different price/cost rates,
and to add a Beancount formatter.

oxrlib/commands/historical.py

@@ -12,15 +12,18 @@ except ImportError:
     import enum34 as enum
 
 class Formatter:
-    def __init__(self, rate, signed_currencies=(), base_fmt='#,##0.###'):
+    def __init__(self, rate, signed_currencies=(), base_fmt='#,##0.###',
+                 rate_precision=5, denomination=None):
         self.rate = rate
         self.base_fmt = base_fmt
         self.base_fmt_noprec = base_fmt.rsplit('.', 1)[0]
         self.signed_currencies = set(code for code in signed_currencies
                                      if self.can_sign_currency(code))
+        self.rate_prec = rate_precision
+        self.denomination = denomination
 
     def can_sign_currency(self, code):
-        return len(babel.numbers.get_currency_symbol(code)) == 1
+        return False
 
     def format_currency(self, amount, code, currency_digits=True):
         if currency_digits:
@@ -37,6 +40,9 @@ class Formatter:
         amt_s = babel.numbers.format_currency(amount, currency, '###0.###')
         return decimal.Decimal(amt_s)
 
+    def normalize_rate(self, rate, prec=None):
+        return rate
+
     def format_rate(self, rate):
         return "{:g}".format(rate)
 
@@ -64,11 +70,8 @@ class Formatter:
 
 
 class LedgerFormatter(Formatter):
-    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 can_sign_currency(self, code):
+        return len(babel.numbers.get_currency_symbol(code)) == 1
 
     def normalize_rate(self, rate, prec=None):
         if prec is None:
@@ -150,11 +153,11 @@ def run(config, stdout, stderr):
         rate = oxrrate.Rate.from_json_file(rate_json)
     if loaders.should_cache():
         config.cache.save_rate(rate)
-    if config.args.output_format is Formats.LEDGER:
-        formatter = LedgerFormatter(rate, config.args.signed_currencies,
-                                    denomination=config.args.denomination)
-    else:
-        formatter = Formatter(rate)
+    formatter = config.args.output_format.value(
+        rate,
+        config.args.signed_currencies,
+        denomination=config.args.denomination,
+    )
     if not config.args.from_currency:
         for from_curr in sorted(rate.rates):
             print(formatter.format_rate_pair_bidir(from_curr, config.args.to_currency),