Data commit

Task/Stack/Python/stack-3.py

@@ -0,0 +1,12 @@
+class Stack:
+    def __init__(self):
+        self._first = None
+    def __nonzero__(self):
+        return self._first is not None
+    def append(self, value):
+        self._first = (value, self._first)
+    def pop(self):
+        if self._first is None:
+            raise IndexError, "pop from empty stack"
+        value, self._first = self._first
+        return value