Revendor editor and make dateutil optional

Re-implemented the ``python-editor`` dependency as a small internal
function to avoid the need for external dependencies.
The implementation is based on the original
version in 7b91b325ff43a0e9235e0f15b57391fa92352626.

Make the ``python-dateutil`` library an optional dependency.
This library is only required if the ``timezone`` option
is used in the Alembic configuration.
An extra require named ``tz`` is available with
``pip install alembic[tz]`` to install it.

Fixes: #674
Fixes: #856
Change-Id: I07f17b2fea01e3a3d677ce95333fe3e8d8d438fd

1 files changed, 16 insertions, 0 deletions

diff --git a/tests/test_script_production.py b/tests/test_script_production.py
index 15d9366..2edae26 100644
--- a/tests/test_script_production.py
+++ b/tests/test_script_production.py
@@ -15,6 +15,7 @@ from alembic.script import ScriptDirectory
 from alembic.testing import assert_raises_message
 from alembic.testing import assertions
 from alembic.testing import eq_
+from alembic.testing import expect_raises_message
 from alembic.testing import is_
 from alembic.testing import mock
 from alembic.testing import ne_
@@ -34,6 +35,10 @@ from alembic.testing.env import write_script
 from alembic.testing.fixtures import TestBase
 from alembic.util import CommandError
 
+try:
+    from unittest.mock import patch
+except ImportError:
+    from mock import patch  # noqa
 env, abc, def_ = None, None, None
 
 
@@ -250,6 +255,17 @@ class ScriptNamingTest(TestBase):
             datetime.datetime(2012, 7, 25, 15, 8, 5),
         )
 
+    def test_no_dateutil_module(self):
+        with patch("alembic.script.base.tz", new=None):
+            with expect_raises_message(
+                CommandError, "The library 'python-dateutil' is required"
+            ):
+                self._test_tz(
+                    "utc",
+                    datetime.datetime(2012, 7, 25, 15, 8, 5),
+                    datetime.datetime(2012, 7, 25, 15, 8, 5),
+                )
+
 
 class RevisionCommandTest(TestBase):
     def setUp(self):