Update git-show recipe

docs/recipes/git-show.rst

@@ -31,7 +31,7 @@ Show SHA hash
 Show diff
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-    >>> diff = commit.tree.diff()
+    >>> diff = repo.diff(commit.parents[0], commit)
 
 ======================================================================
 Show all files in commit
@@ -40,6 +40,52 @@ Show all files in commit
     >>> for e in commit.tree:
     >>>     print(e.name)
 
+======================================================================
+Produce something like a ``git show`` message
+======================================================================
+
+In order to display time zone information you have to create a subclass
+of tzinfo. In Python 3.2+ you can do this fairly directly. In older
+versions you have to make your own class as described in the `Python
+datetime documentation`_::
+
+    from datetime import tzinfo, timedelta
+    class FixedOffset(tzinfo):
+        """Fixed offset in minutes east from UTC."""
+
+        def __init__(self, offset):
+            self.__offset = timedelta(minutes = offset)
+
+        def utcoffset(self, dt):
+            return self.__offset
+
+        def tzname(self, dt):
+            return None # we don't know the time zone's name
+
+        def dst(self, dt):
+            return timedelta(0) # we don't know about DST
+
+.. _Python datetime documentation: https://docs.python.org/2/library/datetime.html#tzinfo-objects
+
+Then you can make your message:
+
+    >>> # Until Python 2.7.9:
+    >>> from __future__ import unicode_literals
+    >>> from datetime import datetime
+    >>> tzinfo  = FixedOffset(commit.author.offset)
+
+    >>> # From Python 3.2:
+    >>> from datetime import datetime, timezone, timedelta
+    >>> tzinfo  = timezone( timedelta(minutes=commit.author.offset) )
+    >>>
+    >>> dt      = datetime.fromtimestamp(float(commit.author.time), tzinfo)
+    >>> timestr = dt.strftime('%c %z')
+    >>> msg     = '\n'.join(['commit {}'.format(commit.tree_id.hex),
+    ...                      'Author: {} <{}>'.format(commit.author.name, commit.author.email),
+    ...                      'Date:   {}'.format(timestr),
+    ...                      '',
+    ...                      commit.message])
+
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 References
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