1 files changed, 168 insertions, 0 deletions
diff --git a/pytz/lazy.py b/pytz/lazy.py
new file mode 100644
index 0000000..f7fc597
--- /dev/null
+++ b/pytz/lazy.py
@@ -0,0 +1,168 @@
+from threading import RLock
+try:
+    from UserDict import DictMixin
+except ImportError:
+    from collections import Mapping as DictMixin
+
+
+# With lazy loading, we might end up with multiple threads triggering
+# it at the same time. We need a lock.
+_fill_lock = RLock()
+
+
+class LazyDict(DictMixin):
+    """Dictionary populated on first use."""
+    data = None
+    def __getitem__(self, key):
+        if self.data is None:
+            _fill_lock.acquire()
+            try:
+                if self.data is None:
+                    self._fill()
+            finally:
+                _fill_lock.release()
+        return self.data[key.upper()]
+
+    def __contains__(self, key):
+        if self.data is None:
+            _fill_lock.acquire()
+            try:
+                if self.data is None:
+                    self._fill()
+            finally:
+                _fill_lock.release()
+        return key in self.data
+
+    def __iter__(self):
+        if self.data is None:
+            _fill_lock.acquire()
+            try:
+                if self.data is None:
+                    self._fill()
+            finally:
+                _fill_lock.release()
+        return iter(self.data)
+
+    def __len__(self):
+        if self.data is None:
+            _fill_lock.acquire()
+            try:
+                if self.data is None:
+                    self._fill()
+            finally:
+                _fill_lock.release()
+        return len(self.data)
+
+    def keys(self):
+        if self.data is None:
+            _fill_lock.acquire()
+            try:
+                if self.data is None:
+                    self._fill()
+            finally:
+                _fill_lock.release()
+        return self.data.keys()
+
+
+class LazyList(list):
+    """List populated on first use."""
+
+    _props = [
+        '__str__', '__repr__', '__unicode__',
+        '__hash__', '__sizeof__', '__cmp__',
+        '__lt__', '__le__', '__eq__', '__ne__', '__gt__', '__ge__',
+        'append', 'count', 'index', 'extend', 'insert', 'pop', 'remove',
+        'reverse', 'sort', '__add__', '__radd__', '__iadd__', '__mul__',
+        '__rmul__', '__imul__', '__contains__', '__len__', '__nonzero__',
+        '__getitem__', '__setitem__', '__delitem__', '__iter__',
+        '__reversed__', '__getslice__', '__setslice__', '__delslice__']
+
+    def __new__(cls, fill_iter=None):
+
+        if fill_iter is None:
+            return list()
+
+        # We need a new class as we will be dynamically messing with its
+        # methods.
+        class LazyList(list):
+            pass
+
+        fill_iter = [fill_iter]
+
+        def lazy(name):
+            def _lazy(self, *args, **kw):
+                _fill_lock.acquire()
+                try:
+                    if len(fill_iter) > 0:
+                        list.extend(self, fill_iter.pop())
+                        for method_name in cls._props:
+                            delattr(LazyList, method_name)
+                finally:
+                    _fill_lock.release()
+                return getattr(list, name)(self, *args, **kw)
+            return _lazy
+
+        for name in cls._props:
+            setattr(LazyList, name, lazy(name))
+
+        new_list = LazyList()
+        return new_list
+
+# Not all versions of Python declare the same magic methods.
+# Filter out properties that don't exist in this version of Python
+# from the list.
+LazyList._props = [prop for prop in LazyList._props if hasattr(list, prop)]
+
+
+class LazySet(set):
+    """Set populated on first use."""
+
+    _props = (
+        '__str__', '__repr__', '__unicode__',
+        '__hash__', '__sizeof__', '__cmp__',
+        '__lt__', '__le__', '__eq__', '__ne__', '__gt__', '__ge__',
+        '__contains__', '__len__', '__nonzero__',
+        '__getitem__', '__setitem__', '__delitem__', '__iter__',
+        '__sub__', '__and__', '__xor__', '__or__',
+        '__rsub__', '__rand__', '__rxor__', '__ror__',
+        '__isub__', '__iand__', '__ixor__', '__ior__',
+        'add', 'clear', 'copy', 'difference', 'difference_update',
+        'discard', 'intersection', 'intersection_update', 'isdisjoint',
+        'issubset', 'issuperset', 'pop', 'remove',
+        'symmetric_difference', 'symmetric_difference_update',
+        'union', 'update')
+
+    def __new__(cls, fill_iter=None):
+
+        if fill_iter is None:
+            return set()
+
+        class LazySet(set):
+            pass
+
+        fill_iter = [fill_iter]
+
+        def lazy(name):
+            def _lazy(self, *args, **kw):
+                _fill_lock.acquire()
+                try:
+                    if len(fill_iter) > 0:
+                        for i in fill_iter.pop():
+                            set.add(self, i)
+                        for method_name in cls._props:
+                            delattr(LazySet, method_name)
+                finally:
+                    _fill_lock.release()
+                return getattr(set, name)(self, *args, **kw)
+            return _lazy
+
+        for name in cls._props:
+            setattr(LazySet, name, lazy(name))
+
+        new_set = LazySet()
+        return new_set
+
+# Not all versions of Python declare the same magic methods.
+# Filter out properties that don't exist in this version of Python
+# from the list.
+LazySet._props = [prop for prop in LazySet._props if hasattr(set, prop)]