Use datetime by default to format log time

Change logging time formatting to allow using datetime.strftime and
change the default converter to create a datetime that can contain more
information than the time tuple of the default converter. This allows
for having `datefmt` template strings that can use microseconds as part
of it.

Lib/logging/__init__.py

@@ -25,6 +25,7 @@
 
 import sys, os, time, io, re, traceback, warnings, weakref, collections.abc
 
+import datetime
 from string import Template
 from string import Formatter as StrFormatter
 
@@ -550,7 +551,7 @@ class Formatter(object):
                         the record is emitted
     """
 
-    converter = time.localtime
+    converter = datetime.datetime.fromtimestamp
 
     def __init__(self, fmt=None, datefmt=None, style='%', validate=True):
         """
@@ -600,10 +601,17 @@ def formatTime(self, record, datefmt=None):
         set the 'converter' attribute in the Formatter class.
         """
         ct = self.converter(record.created)
+
+        try:
+            formatting_function = ct.strftime
+        except AttributeError:
+            def formatting_function(format):
+                return time.strftime(format, ct)
+
         if datefmt:
-            s = time.strftime(datefmt, ct)
+            s = formatting_function(datefmt)
         else:
-            t = time.strftime(self.default_time_format, ct)
+            t = formatting_function(self.default_time_format)
             s = self.default_msec_format % (t, record.msecs)
         return s
 

Lib/test/test_logging.py

@@ -3893,6 +3893,21 @@ def test_time(self):
         f.format(r)
         self.assertEqual(r.asctime, '1993-04-21 08:03:00,123')
 
+    def test_time_datetime_or_time_tiple_format_are_identical(self):
+        r = self.get_record()
+        f1 = logging.Formatter('%(asctime)s')
+        f1.converter = datetime.datetime.fromtimestamp
+        f2 = logging.Formatter('%(asctime)s')
+        f2.converter = time.localtime
+        assert f1.format(r) == f2.format(r)
+
+    def test_time_formatting_of_microsecond(self):
+        r = self.get_record()
+        f = logging.Formatter('%(asctime)s', datefmt="%f")
+        created_microseconds = int(r.created % 1 * 10 ** 6)
+        self.assertEquals(int(f.format(r)), created_microseconds)
+
+
 class TestBufferingFormatter(logging.BufferingFormatter):
     def formatHeader(self, records):
         return '[(%d)' % len(records)