Fixes a non-deterministic failing test in bigquery.

dhermes · dhermes · commit 0f0a3342a454 · 2015-07-31T13:29:45.000-07:00
This has something to do with rounding of floats in
Python 3. For example, .123 gets rounded down when
converted to floating point:

&gt;&gt;&gt; (0.123).hex()
'0x1.f7ced916872b0p-4'
&gt;&gt;&gt; # Add 4 for exponent and multiply .123 by 1000
&gt;&gt;&gt; 2**(52 + 4) * 123  # Add 4 for exponent and multiply .123 by 1000
8863084066665136128
&gt;&gt;&gt; # Account for the factor of 1000 we've multiplied .123 by
&gt;&gt;&gt; (0x1f7ced916872b0) * 1000
8863084066665136000
diff --git a/gcloud/bigquery/_helpers.py b/gcloud/bigquery/_helpers.py
@@ -42,8 +42,12 @@ def _datetime_from_prop(value):
     """
     if value is not None:
         # back-end returns timestamps as milliseconds since the epoch
-        value = datetime.datetime.utcfromtimestamp(value / 1000.0)
-        return value.replace(tzinfo=pytz.utc)
+        seconds = int(value / 1000.0)
+        microseconds = 1000.0 * (value - 1000 * seconds)
+        return (
+            _EPOCH +
+            datetime.timedelta(seconds=seconds, microseconds=microseconds)
+        )
 
 
 def _prop_from_datetime(value):
