add IPython.utils.tz

Basic support for tz-aware UTC methods on date time objects.

The raw `utcfoo` methods still produce naïve objects,
so they are wrapped in a simple zero-offset tz-aware object.

This allows jsonutil to publish the timezone info,
eliminating the ambiguity of naïve timestamps (Firefox assumes local time, WebKit UTC).

IPython/utils/tz.py

@@ -0,0 +1,46 b''
+# encoding: utf-8
+"""
+Timezone utilities
+
+Just UTC-awareness right now
+"""
+
+#-----------------------------------------------------------------------------
+#  Copyright (C) 2013 The IPython Development Team
+#
+#  Distributed under the terms of the BSD License.  The full license is in
+#  the file COPYING, distributed as part of this software.
+#-----------------------------------------------------------------------------
+
+#-----------------------------------------------------------------------------
+# Imports
+#-----------------------------------------------------------------------------
+
+from datetime import tzinfo, timedelta, datetime
+
+#-----------------------------------------------------------------------------
+# Code
+#-----------------------------------------------------------------------------
+# constant for zero offset
+ZERO = timedelta(0)
+
+class tzUTC(tzinfo):
+    """tzinfo object for UTC (zero offset)"""
+
+    def utcoffset(self, d):
+        return ZERO
+
+    def dst(self, d):
+        return ZERO
+
+UTC = tzUTC()
+
+def utc_aware(unaware):
+    """decorator for adding UTC tzinfo to datetime's utcfoo methods"""
+    def utc_method(*args, **kwargs):
+        dt = unaware(*args, **kwargs)
+        return dt.replace(tzinfo=UTC)
+    return utc_method
+
+utcfromtimestamp = utc_aware(datetime.utcfromtimestamp)
+utcnow = utc_aware(datetime.utcnow)