Fixed #11206 -- Ensure that the floatformat template filter doesn't switch to…

Fixed #11206 -- Ensure that the floatformat template filter doesn't switch to scientific notation when asked to format a zero value with more than six decimal places. Thanks Tai Lee for the report and fix and Facundo Batista for his help when Decimal module expertise was needed.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15736 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/template/defaultfilters.py

@@ -149,9 +149,19 @@ def floatformat(text, arg=-1):
     if p == 0:
         exp = Decimal(1)
     else:
-        exp = Decimal('1.0') / (Decimal(10) ** abs(p))
+        exp = Decimal(u'1.0') / (Decimal(10) ** abs(p))
     try:
-        return mark_safe(formats.number_format(u'%s' % str(d.quantize(exp, ROUND_HALF_UP)), abs(p)))
+        # Avoid conversion to scientific notation by accessing `sign`, `digits`
+        # and `exponent` from `Decimal.as_tuple()` directly.
+        sign, digits, exponent = d.quantize(exp, ROUND_HALF_UP).as_tuple()
+        digits = [unicode(digit) for digit in reversed(digits)]
+        while len(digits) <= abs(exponent):
+            digits.append(u'0')
+        digits.insert(-exponent, u'.')
+        if sign:
+            digits.append(u'-')
+        number = u''.join(reversed(digits))
+        return mark_safe(formats.number_format(number, abs(p)))
     except InvalidOperation:
         return input_val
 floatformat.is_safe = True

tests/regressiontests/defaultfilters/tests.py

 # -*- coding: utf-8 -*-
 import datetime
-import unittest
+from django.utils import unittest
 
 from django.template.defaultfilters import *
 
@@ -29,6 +29,13 @@ class DefaultFiltersTests(unittest.TestCase):
         self.assertEqual(floatformat(u'¿Cómo esta usted?'), u'')
         self.assertEqual(floatformat(None), u'')
 
+        # Check that we're not converting to scientific notation.
+        self.assertEqual(floatformat(0, 6), u'0.000000')
+        self.assertEqual(floatformat(0, 7), u'0.0000000')
+        self.assertEqual(floatformat(0, 10), u'0.0000000000')
+        self.assertEqual(floatformat(0.000000000000000000015, 20),
+                                     u'0.00000000000000000002')
+
         pos_inf = float(1e30000)
         self.assertEqual(floatformat(pos_inf), unicode(pos_inf))
 
@@ -46,6 +53,13 @@ class DefaultFiltersTests(unittest.TestCase):
 
         self.assertEqual(floatformat(FloatWrapper(11.000001), -2), u'11.00')
 
+    # This fails because of Python's float handling. Floats with many zeroes
+    # after the decimal point should be passed in as another type such as
+    # unicode or Decimal.
+    @unittest.expectedFailure
+    def test_floatformat_fail(self):
+        self.assertEqual(floatformat(1.00000000000000015, 16), u'1.0000000000000002')
+
     def test_addslashes(self):
         self.assertEqual(addslashes(u'"double quotes" and \'single quotes\''),
                           u'\\"double quotes\\" and \\\'single quotes\\\'')