Math: Round trailing nines up in @convert

Author: progval

plugins/Math/plugin.py

@@ -253,6 +253,7 @@ def convert(self, irc, msg, args, number, unit1, unit2):
             digits = len(str(number).split('.')[1])
         except IndexError:
             digits = 0
+
         try:
             newNum = convertcore.convert(number, unit1, unit2)
             if isinstance(newNum, float):
@@ -261,11 +262,23 @@ def convert(self, irc, msg, args, number, unit1, unit2):
                     if char != '0':
                         break
                     zeros += 1
+
                 # Let's add one signifiant digit. Physicists would not like
                 # that, but common people usually do not give extra zeros...
                 # (for example, with '32 C to F', an extra digit would be
                 # expected).
                 newNum = round(newNum, digits + 1 + zeros)
+
+                # However, if the difference is negligeable compared to the
+                # precision we got in the input, we remove two more digits.
+                # this is useful for rounding .9999999 up.
+                newNum2 = round(newNum, digits - 1 + zeros)
+                try:
+                    if abs((newNum2 - newNum) / newNum) < 10**(-digits-10):
+                        newNum = newNum2
+                except ZeroDivisionError:
+                    pass
+
             newNum = self._floatToString(newNum)
             irc.reply(str(newNum))
         except convertcore.UnitDataError as ude:

plugins/Math/test.py

@@ -188,6 +188,13 @@ def testConvert(self):
         self.assertError('convert 1 mol to grams')
         self.assertError('convert 1 m to kpa')
 
+    def testConvertSignificantDigits(self):
+        self.assertResponse('convert 1 s to ns', '1000000000')
+        self.assertResponse('convert 0.9999999999999999 s to ns',
+                            '999999999.9999999')
+        self.assertResponse('convert 1000000000 ns to s', '1')
+        self.assertResponse('convert 999999999.9999999 ns to s', '1')
+
     def testConvertSingularPlural(self):
         self.assertResponse('convert [calc 2*pi] rads to degrees', '360')
         self.assertResponse('convert 1 carat to grams', '0.2')