fix(commit): serialization timezone handling

Previously timezones which were not divisable by 3600s would be
parsed correctly, but would serialize into a full hour, rounded up.

Now floating point computation is used which fixes the issue.

Related to #336

Author: Byron

doc/source/changes.rst

@@ -2,6 +2,13 @@
 Changelog
 =========
 
+1.0.2 - Fixes
+=============
+
+* CRITICAL: fixed incorrect `Commit` object serialization when authored or commit date had timezones which were not
+  divisable by 3600 seconds. This would happen if the timezone was something like `+0530` for instance.
+* A list of all additional fixes can be found `on github <https://github.com/gitpython-developers/GitPython/issues?q=milestone%3A%22v1.0.2+-+Fixes%22+is%3Aclosed>`_
+
 1.0.1 - Fixes
 =============
 

git/objects/util.py

@@ -73,7 +73,7 @@ def utctz_to_altz(utctz):
 def altz_to_utctz_str(altz):
     """As above, but inverses the operation, returning a string that can be used
     in commit objects"""
-    utci = -1 * int((altz / 3600) * 100)
+    utci = -1 * int((float(altz) / 3600) * 100)
     utcs = str(abs(utci))
     utcs = "0" * (4 - len(utcs)) + utcs
     prefix = (utci < 0 and '-') or '+'

git/test/performance/test_commit.py

@@ -76,7 +76,7 @@ def test_commit_iteration(self):
               % (nc, elapsed_time, nc / elapsed_time), file=sys.stderr)
 
     def test_commit_serialization(self):
-        assert_commit_serialization(self.gitrwrepo, self.gitrwrepo.head, True)
+        assert_commit_serialization(self.gitrwrepo, '58c78e6', True)
 
         rwrepo = self.gitrwrepo
         make_object = rwrepo.odb.store