Add support for a timezone type.

setup.py

@@ -42,7 +42,8 @@ extras_require = {
     ],
     'password': ['passlib >= 1.6, < 2.0'],
     'color': ['colour>=0.0.4'],
-    'ipaddress': ['ipaddr'] if not PY3 else []
+    'ipaddress': ['ipaddr'] if not PY3 else [],
+    'timezone': ['python-dateutil']
 }
 
 

sqlalchemy_utils/types/timezone.py

@@ -0,0 +1,74 @@
+import six
+from sqlalchemy import types
+from sqlalchemy_utils import ImproperlyConfigured
+
+
+class TimezoneType(types.TypeDecorator):
+    """
+    Changes Timezone objects to a string representation on the way in and
+    changes them back to Timezone objects on the way out.
+    """
+
+    impl = types.CHAR(50)
+
+    python_type = None
+
+    def __init__(self, backend='dateutil'):
+        """
+        :param backend: Whether to use 'dateutil' or 'pytz' for timezones.
+        """
+
+        self.backend = backend
+        if backend == 'dateutil':
+            try:
+                from dateutil.tz import tzfile
+                from dateutil.zoneinfo import gettz
+
+                self.python_type = tzfile
+                self._to = gettz
+                self._from = lambda x: x._filename
+
+            except ImportError:
+                raise ImproperlyConfigured(
+                    "'python-dateutil' is required to use the "
+                    "'dateutil' backend for 'TimezoneType'"
+                )
+
+        elif backend == 'pytz':
+            try:
+                from pytz import tzfile, timezone
+
+                self.python_type = tzfile.DstTzInfo
+                self._to = timezone
+                self._from = six.text_type
+
+            except ImportError:
+                raise ImproperlyConfigured(
+                    "'pytz' is required to use the 'pytz' backend "
+                    "for 'TimezoneType'"
+                )
+
+        else:
+            raise ImproperlyConfigured(
+                "'pytz' or 'dateutil' are the backends supported for "
+                "'TimezoneType'"
+            )
+
+    def _coerce(self, value):
+        if value and not isinstance(value, self.python_type):
+            obj = self._to(value)
+            if obj is None:
+                raise ValueError("unknown time zone '%s'" % value)
+
+            return obj
+
+        return value
+
+    def coercion_listener(self, target, value, oldvalue, initiator):
+        return self._coerce(value)
+
+    def process_bind_param(self, value, dialect):
+        return self._from(self._coerce(value)) if value else None
+
+    def process_result_value(self, value, dialect):
+        return self._to(value) if value else None

tests/test_timezone.py

@@ -0,0 +1,39 @@
+from pytest import mark
+import six
+import sqlalchemy as sa
+from sqlalchemy_utils.types import timezone
+from tests import TestCase
+
+
+try:
+    import dateutil
+
+except ImportError:
+    dateutil = None
+
+
+@mark.skipif('dateutil is None')
+class TestIPAddressType(TestCase):
+    def create_models(self):
+        class Visitor(self.Base):
+            __tablename__ = 'document'
+            id = sa.Column(sa.Integer, primary_key=True)
+            timezone = sa.Column(timezone.TimezoneType)
+
+            def __repr__(self):
+                return 'Visitor(%r)' % self.id
+
+        self.Visitor = Visitor
+
+    def test_parameter_processing(self):
+        visitor = self.Visitor(
+            timezone=u'America/Los_Angeles'
+        )
+
+        self.session.add(visitor)
+        self.session.commit()
+
+        visitor = self.session.query(self.Visitor).filter_by(
+            timezone='America/Los_Angeles').first()
+
+        assert visitor is not None