Fix for Bug #5, daterange not accepting subclasses of date

doc/changelog.rst

@@ -4,6 +4,14 @@ Version are structured like the following: ``<major>.<minor>.<bugfix>``. The
 first `0.1` release does not properly adhere to this. Unless explicitly stated,
 changes are made by `Andreas Runfalk <https://github.com/runfalk>`_.
 
+Version 0.4.0
+-------------
+Released on <unreleased>
+
+- Fixed :class:`~spans.types.daterange` not accepting subclasses of ``date``
+  (`bug #5 <https://github.com/runfalk/spans/issues/5>`_)
+
+
 Version 0.3.0
 -------------
 Released on 26th August, 2016

spans/tests/test_types.py

@@ -383,6 +383,16 @@ def test_len(self):
         with self.assertRaises(ValueError):
             len(daterange())
 
+    def test_bug5_date_subclassing(self):
+        """
+        `Bug #5 <https://github.com/runfalk/spans/issues/5>`
+        """
+
+        class DateSubClass(date):
+            pass
+
+        daterange(DateSubClass(2000, 1, 1))
+
 
 class TestStrRange(TestCase):
     def test_last(self):

spans/types.py

@@ -938,6 +938,22 @@ def prev(cls, curr):
         else:
             return curr[:-1] + uchr(ord(curr[-1]) - 1)
 
+
+def _is_valid_date(obj, accept_none=True):
+    """
+    Check if an object is an instance of, or a subclass deriving from, a
+    ``date``. However, it does not consider ``datetime`` or subclasses thereof
+    as valid dates.
+
+    :param obj: Object to test as date.
+    :param accept_none: If True None is considered as a valid date object.
+    """
+
+    if accept_none and obj is None:
+        return True
+    return isinstance(obj, date) and not isinstance(obj, datetime)
+
+
 class daterange(discreterange, offsetablerange):
     """
     Range that operates on ``datetime.date``.
@@ -961,14 +977,14 @@ class daterange(discreterange, offsetablerange):
     step = timedelta(days=1)
 
     def __init__(self, lower=None, upper=None, lower_inc=None, upper_inc=None):
-        if lower is not None and type(lower) is not date:
+        if not _is_valid_date(lower, accept_none=True):
             raise TypeError((
                 "Invalid type for lower bound '{lower_type.__name__}'"
                 " expected '{expected_type.__name__}'").format(
                     expected_type=self.type,
                     lower_type=lower.__class__))
 
-        if upper is not None and type(upper) is not date:
+        if not _is_valid_date(upper, accept_none=True):
             raise TypeError((
                 "Invalid type for upper bound '{upper_type.__name__}'"
                 " expected '{expected_type.__name__}'").format(