8th day of python challenges 111-117

venv/lib/python3.6/site-packages/dateutil/tz/_factories.py

@@ -0,0 +1,73 @@
+from datetime import timedelta
+import weakref
+from collections import OrderedDict
+
+
+class _TzSingleton(type):
+    def __init__(cls, *args, **kwargs):
+        cls.__instance = None
+        super(_TzSingleton, cls).__init__(*args, **kwargs)
+
+    def __call__(cls):
+        if cls.__instance is None:
+            cls.__instance = super(_TzSingleton, cls).__call__()
+        return cls.__instance
+
+
+class _TzFactory(type):
+    def instance(cls, *args, **kwargs):
+        """Alternate constructor that returns a fresh instance"""
+        return type.__call__(cls, *args, **kwargs)
+
+
+class _TzOffsetFactory(_TzFactory):
+    def __init__(cls, *args, **kwargs):
+        cls.__instances = weakref.WeakValueDictionary()
+        cls.__strong_cache = OrderedDict()
+        cls.__strong_cache_size = 8
+
+    def __call__(cls, name, offset):
+        if isinstance(offset, timedelta):
+            key = (name, offset.total_seconds())
+        else:
+            key = (name, offset)
+
+        instance = cls.__instances.get(key, None)
+        if instance is None:
+            instance = cls.__instances.setdefault(key,
+                                                  cls.instance(name, offset))
+
+        cls.__strong_cache[key] = cls.__strong_cache.pop(key, instance)
+
+        # Remove an item if the strong cache is overpopulated
+        # TODO: Maybe this should be under a lock?
+        if len(cls.__strong_cache) > cls.__strong_cache_size:
+            cls.__strong_cache.popitem(last=False)
+
+        return instance
+
+
+class _TzStrFactory(_TzFactory):
+    def __init__(cls, *args, **kwargs):
+        cls.__instances = weakref.WeakValueDictionary()
+        cls.__strong_cache = OrderedDict()
+        cls.__strong_cache_size = 8
+
+    def __call__(cls, s, posix_offset=False):
+        key = (s, posix_offset)
+        instance = cls.__instances.get(key, None)
+
+        if instance is None:
+            instance = cls.__instances.setdefault(key,
+                cls.instance(s, posix_offset))
+
+        cls.__strong_cache[key] = cls.__strong_cache.pop(key, instance)
+
+
+        # Remove an item if the strong cache is overpopulated
+        # TODO: Maybe this should be under a lock?
+        if len(cls.__strong_cache) > cls.__strong_cache_size:
+            cls.__strong_cache.popitem(last=False)
+
+        return instance
+