- round down microseconds (in case precision is higher)

4 files changed, 16 insertions, 7 deletions

diff --git a/CHANGES.txt b/CHANGES.txt
index 1bac7d5..3f4191e 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -7,6 +7,7 @@ CHANGES
 
 - drop end of life python versions
 - Don't match garbage characters at the end of parsed strings #16 (Gabriel de Perthuis)
+- Breaking: fractional seconds are cut off to microseconds (round down)
 
 
 0.6.1 (2021-12-13)
diff --git a/src/isodate/isotime.py b/src/isodate/isotime.py
index 3e2bb46..470c5b6 100644
--- a/src/isodate/isotime.py
+++ b/src/isodate/isotime.py
@@ -6,7 +6,7 @@ It supports all basic and extended formats including time zone specifications
 as described in the ISO standard.
 """
 import re
-from decimal import Decimal
+from decimal import Decimal, ROUND_FLOOR
 from datetime import time
 
 from isodate.isostrf import strftime, TIME_EXT_COMPLETE, TZ_EXT
@@ -102,8 +102,9 @@ def parse_time(timestring):
                 int(groups["tzmin"] or 0),
             )
             if "second" in groups:
-                # round to microseconds if fractional seconds are more precise
-                second = Decimal(groups["second"]).quantize(Decimal(".000001"))
+                second = Decimal(groups["second"]).quantize(
+                    Decimal(".000001"), rounding=ROUND_FLOOR
+                )
                 microsecond = (second - int(second)) * int(1e6)
                 # int(...) ... no rounding
                 # to_integral() ... rounding
@@ -116,7 +117,9 @@ def parse_time(timestring):
                 )
             if "minute" in groups:
                 minute = Decimal(groups["minute"])
-                second = (minute - int(minute)) * 60
+                second = Decimal((minute - int(minute)) * 60).quantize(
+                    Decimal(".000001"), rounding=ROUND_FLOOR
+                )
                 microsecond = (second - int(second)) * int(1e6)
                 return time(
                     int(groups["hour"]),
diff --git a/src/isodate/tests/test_datetime.py b/src/isodate/tests/test_datetime.py
index 465654e..19752d3 100644
--- a/src/isodate/tests/test_datetime.py
+++ b/src/isodate/tests/test_datetime.py
@@ -105,9 +105,9 @@ TEST_CASES = [
     ),
     (
         "2012-10-30T08:55:22.1234567Z",
-        datetime(2012, 10, 30, 8, 55, 22, 123457, tzinfo=UTC),
+        datetime(2012, 10, 30, 8, 55, 22, 123456, tzinfo=UTC),
         DATE_EXT_COMPLETE + "T" + TIME_EXT_COMPLETE + ".%f" + TZ_BAS,
-        "2012-10-30T08:55:22.123457Z",
+        "2012-10-30T08:55:22.123456Z",
     ),
     (
         "2012-10-30T08:55:22.1234561Z",
diff --git a/src/isodate/tests/test_time.py b/src/isodate/tests/test_time.py
index d369714..c843bc9 100644
--- a/src/isodate/tests/test_time.py
+++ b/src/isodate/tests/test_time.py
@@ -24,7 +24,12 @@ TEST_CASES = [
     # test precision
     ("15:33:42.123456", time(15, 33, 42, 123456), None),
     ("15:33:42.1234564", time(15, 33, 42, 123456), None),
-    ("15:33:42.1234557", time(15, 33, 42, 123456), None),
+    ("15:33:42.1234557", time(15, 33, 42, 123455), None),
+    (
+        "10:59:59.9999999Z",
+        time(10, 59, 59, 999999, tzinfo=UTC),
+        None,
+    ),  # TIME_EXT_COMPLETE + TZ_EXT),
     ("2320,8", time(23, 20, 48), None),
     ("23:20,8", time(23, 20, 48), None),
     ("23,3", time(23, 18), None),