Add utils module

fimfarchive/utils.py

@@ -0,0 +1,45 @@
+"""
+Various utilities.
+"""
+
+
+#
+# Fimfarchive, preserves stories from Fimfiction.
+# Copyright (C) 2015  Joakim Soderlund
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+
+__all__ = (
+    'Empty',
+)
+
+
+class EmptyMeta(type):
+    """
+    Meta-class for Empty.
+    """
+
+    def __bool__(cls):
+        return False
+
+
+class Empty(metaclass=EmptyMeta):
+    """
+    Unique placeholder similar to `None`.
+    """
+
+    def __bool__(self):
+        return False

tests/test_utils.py

@@ -0,0 +1,71 @@
+"""
+Utility tests.
+"""
+
+
+#
+# Fimfarchive, preserves stories from Fimfiction.
+# Copyright (C) 2015  Joakim Soderlund
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+
+from fimfarchive.utils import Empty
+
+
+class TestEmpty:
+    """
+    Empty tests.
+    """
+
+    def test_empty_class_is_not_none(self):
+        """
+        Tests `Empty` class is different from `None`.
+        """
+        assert Empty is not None
+        assert Empty != None  # noqa
+
+    def test_empty_class_evaluates_to_false(self):
+        """
+        Tests `Empty` class evaluates to `False`.
+        """
+        assert not Empty
+
+    def test_empty_class_is_empty(self):
+        """
+        Tests `Empty` class can be identified.
+        """
+        assert Empty is Empty
+        assert Empty == Empty
+
+    def test_empty_instance_evaluates_to_false(self):
+        """
+        Tests `Empty` instance evaulates to `False`
+        """
+        assert not Empty()
+
+    def test_empty_instance_is_unique(self):
+        """
+        Tests `Empty` instances are unique.
+        """
+        empty = Empty()
+
+        assert isinstance(empty, Empty)
+        assert empty is not Empty
+        assert empty != Empty
+        assert empty is not Empty()
+        assert empty != Empty()
+        assert empty is empty
+        assert empty == empty