Fixes to support Python 2.6 again.

Details:

- Replaced the use of dictionary comprehensions in `git/cmd.py` around
  line 800 with the code before that change (in commit 25a2ebf).
  Reason: dict comprehensions were introduced only in Python 2.7.

- Changed the import source for `SkipTest` and `skipIf` from `unittest.case`
  to first trying `unittest` and upon ImportError from `unittest2`.
  This was done in `git/util.py` and in several testcases.
  Reason: `SkipTest` and `skipIf` were introduced to unittest only
  in Python 2.7, and `unittest2` is a backport of `unittest` additions
  to Python 2.6.

- In git/test/lib/helper.py, fixed the definition of `assertRaisesRegex`
  to work on py26.

- For Python 2.6, added the `unittest2` dependency to `requirements.txt`
  and changed Travis control file to install `unittest2`.

Author: andy-maier

Diff for: .travis.yml

@@ -18,6 +18,7 @@ install:
   - git submodule update --init --recursive
   - git fetch --tags
   - pip install codecov flake8 ddt sphinx
+  - if [ "$TRAVIS_PYTHON_VERSION" == '2.6' ]; then pip install unittest2; fi
 
   # generate some reflog as git-python tests need it (in master)
   - ./init-tests-after-clone.sh

Diff for: git/cmd.py

@@ -812,8 +812,12 @@ def _call_process(self, method, *args, **kwargs):
         :return: Same as ``execute``"""
         # Handle optional arguments prior to calling transform_kwargs
         # otherwise these'll end up in args, which is bad.
-        _kwargs = {k: v for k, v in kwargs.items() if k in execute_kwargs}
-        kwargs = {k: v for k, v in kwargs.items() if k not in execute_kwargs}
+        _kwargs = dict()
+        for kwarg in execute_kwargs:
+            try:
+                _kwargs[kwarg] = kwargs.pop(kwarg)
+            except KeyError:
+                pass
 
         insert_after_this_arg = kwargs.pop('insert_kwargs_after', None)
 

Diff for: git/objects/submodule/base.py

@@ -38,7 +38,10 @@
 import os
 import logging
 import uuid
-from unittest.case import SkipTest
+try:
+    from unittest import SkipTest
+except ImportError:
+    from unittest2 import SkipTest
 from git.util import HIDE_WINDOWS_KNOWN_ERRORS
 from git.objects.base import IndexObject, Object
 from git.cmd import Git

Diff for: git/test/lib/helper.py

@@ -6,20 +6,24 @@
 from __future__ import print_function
 
 from functools import wraps
+import sys
 import io
 import logging
 import os
 import tempfile
 import textwrap
 import time
-from unittest import TestCase
-import unittest
 
-from git.compat import string_types, is_win, PY3
+from git.compat import string_types, is_win
 from git.util import rmtree
 
 import os.path as osp
+if sys.version_info[0:2] == (2, 6):
+    import unittest2 as unittest
+else:
+    import unittest
 
+TestCase = unittest.TestCase
 
 ospd = osp.dirname
 
@@ -329,8 +333,8 @@ class TestBase(TestCase):
       of the project history ( to assure tests don't fail for others ).
     """
 
-    if not PY3:
-        assertRaisesRegex = unittest.TestCase.assertRaisesRegexp
+    if sys.version_info[0:2] == (2, 7):
+        assertRaisesRegex = TestCase.assertRaisesRegexp
 
     def _small_repo_url(self):
         """:return" a path to a small, clonable repository"""

Diff for: git/test/performance/test_odb.py

@@ -3,7 +3,11 @@
 
 import sys
 from time import time
-from unittest.case import skipIf
+try:
+    from unittest import skipIf
+except ImportError:
+    from unittest2 import skipIf
+
 
 from git.compat import PY3
 from git.util import HIDE_WINDOWS_KNOWN_ERRORS

Diff for: git/test/test_base.py

@@ -7,8 +7,10 @@
 import os
 import sys
 import tempfile
-from unittest import skipIf
-
+try:
+    from unittest import SkipTest, skipIf
+except ImportError:
+    from unittest2 import SkipTest, skipIf
 import git.objects.base as base
 from git.test.lib import (
     TestBase,
@@ -129,7 +131,7 @@ def test_add_unicode(self, rw_repo):
         try:
             file_path.encode(sys.getfilesystemencoding())
         except UnicodeEncodeError:
-            from unittest import SkipTest
+
             raise SkipTest("Environment doesn't support unicode filenames")
 
         with open(file_path, "wb") as fp:

Diff for: git/test/test_index.py

@@ -13,7 +13,10 @@
 )
 import sys
 import tempfile
-from unittest.case import skipIf
+try:
+    from unittest import skipIf
+except ImportError:
+    from unittest2 import skipIf
 
 from git import (
     IndexFile,

Diff for: git/test/test_remote.py

@@ -6,7 +6,10 @@
 
 import random
 import tempfile
-from unittest.case import skipIf
+try:
+    from unittest import skipIf
+except ImportError:
+    from unittest2 import skipIf
 
 from git import (
     RemoteProgress,

Diff for: git/test/test_repo.py

@@ -11,7 +11,10 @@
 import pickle
 import sys
 import tempfile
-from unittest.case import skipIf
+try:
+    from unittest import skipIf, SkipTest
+except ImportError:
+    from unittest2 import skipIf, SkipTest
 
 from git import (
     InvalidGitRepositoryError,
@@ -54,7 +57,6 @@
 from git.test.lib import with_rw_directory
 from git.util import join_path_native, rmtree, rmfile
 from gitdb.util import bin_to_hex
-from unittest import SkipTest
 
 import functools as fnt
 import os.path as osp

Diff for: git/test/test_submodule.py

@@ -2,7 +2,10 @@
 # the BSD License: http://www.opensource.org/licenses/bsd-license.php
 import os
 import sys
-from unittest.case import skipIf
+try:
+    from unittest import skipIf
+except ImportError:
+    from unittest2 import skipIf
 
 import git
 from git.cmd import Git

Diff for: git/test/test_tree.py

@@ -7,7 +7,10 @@
 from io import BytesIO
 import os
 import sys
-from unittest.case import skipIf
+try:
+    from unittest import skipIf
+except ImportError:
+    from unittest2 import skipIf
 
 from git import (
     Tree,

Diff for: git/util.py

@@ -34,8 +34,10 @@
     PY3
 )
 from .exc import InvalidGitRepositoryError
-from unittest.case import SkipTest
-
+try:
+    from unittest import SkipTest
+except ImportError:
+    from unittest2 import SkipTest
 
 # NOTE:  Some of the unused imports might be used/imported by others.
 # Handle once test-cases are back up and running.

Diff for: requirements.txt

@@ -1,3 +1,4 @@
 gitdb>=0.6.4
 ddt
-mock
+mock
+unittest2; python_version < '2.7'