AmountToString should now display without floating point inaccuracies

tipbot/utils.py

@@ -14,6 +14,8 @@ import hashlib
 import json
 import httplib
 import time
+import math
+from decimal import *
 import tipbot.config as config
 import tipbot.coinspecs as coinspecs
 from tipbot.log import log_error, log_warn, log_info, log_log
@@ -77,6 +79,62 @@ def IsValidAddress(address):
       return True
   return False
 
+# Code taken from the Python documentation
+def moneyfmt(value, places=2, curr='', sep=',', dp='.',
+             pos='', neg='-', trailneg=''):
+    """Convert Decimal to a money formatted string.
+
+    places:  required number of places after the decimal point
+    curr:    optional currency symbol before the sign (may be blank)
+    sep:     optional grouping separator (comma, period, space, or blank)
+    dp:      decimal point indicator (comma or period)
+             only specify as blank when places is zero
+    pos:     optional sign for positive numbers: '+', space or blank
+    neg:     optional sign for negative numbers: '-', '(', space or blank
+    trailneg:optional trailing minus indicator:  '-', ')', space or blank
+
+    >>> d = Decimal('-1234567.8901')
+    >>> moneyfmt(d, curr='$')
+    '-$1,234,567.89'
+    >>> moneyfmt(d, places=0, sep='.', dp='', neg='', trailneg='-')
+    '1.234.568-'
+    >>> moneyfmt(d, curr='$', neg='(', trailneg=')')
+    '($1,234,567.89)'
+    >>> moneyfmt(Decimal(123456789), sep=' ')
+    '123 456 789.00'
+    >>> moneyfmt(Decimal('-0.02'), neg='<', trailneg='>')
+    '<0.02>'
+
+    """
+    q = Decimal(10) ** -places      # 2 places --> '0.01'
+    sign, digits, exp = value.quantize(q).as_tuple()
+    result = []
+    digits = map(str, digits)
+    build, next = result.append, digits.pop
+    if sign:
+        build(trailneg)
+    for i in range(places):
+        build(next() if digits else '0')
+    build(dp)
+    if not digits:
+        build('0')
+    i = 0
+    while digits:
+        build(next())
+        i += 1
+        if i == 3 and digits:
+            i = 0
+            build(sep)
+    build(curr)
+    build(neg if sign else pos)
+    s = ''.join(reversed(result))
+
+    if dp in s:
+      s=s.strip('0').rstrip(dp)
+    if s=="" or s[0]==dp:
+      s="0"+s
+    return s
+
 def AmountToString(amount):
   if amount == None:
     amount = 0
@@ -85,12 +143,13 @@ def AmountToString(amount):
   if lamount == 0:
     samount = "0 %s" % coinspecs.name
   else:
+    places=long(0.5+math.log10(coinspecs.atomic_units))
     for den in coinspecs.denominations:
       if lamount < den[0]:
-        samount = "%.16g %s" % (float(lamount) / den[1], den[2])
+        samount = moneyfmt(Decimal(lamount)/Decimal(den[1]),places=places) + " " + den[2]
         break
   if not samount:
-      samount = "%.16g %s" % (float(lamount) / coinspecs.atomic_units, coinspecs.name)
+    samount = moneyfmt(Decimal(lamount)/Decimal(coinspecs.atomic_units),places=places) + " " + coinspecs.name
   return samount
 
 def TimeToString(seconds):