add code example

behavioral/iterator/alpha_order_iterator.py

@@ -0,0 +1,64 @@
+from __future__ import annotations
+
+from typing import Iterator, Iterable, List, Any
+
+
+class WordCollection(Iterable):
+    """
+    Concrete Collections provide one or several methods for retrieving fresh
+    iterator instances, compatible with the collection class.
+    """
+
+    def __init__(self, collection: List[Any] = []) -> None:
+        self._collection = collection
+
+    def __iter__(self) -> AlphabeticalOrderIterator:
+        """
+        The __iter__() method returns the iterator object itself, by default we
+        return the iterator in ascending order.
+        """
+        return AlphabeticalOrderIterator(self._collection)
+
+    def get_reverse_iterator(self) -> AlphabeticalOrderIterator:
+        return AlphabeticalOrderIterator(self._collection, reverse=True)
+
+    def add_item(self, item: Any) -> None:
+        self._collection.append(item)
+
+
+class AlphabeticalOrderIterator(Iterator):
+    """
+    Concrete Iterators implement various traversal algorithms. These classes
+    store the current traversal position at all times.
+    """
+
+    """
+    `_position` attribute stores the current traversal position. An iterator may
+    have a lot of other fields for storing iteration state, especially when it
+    is supposed to work with a particular kind of collection.
+    """
+    _position: int = None
+
+    """
+    This attribute indicates the traversal direction.
+    """
+    _reverse: bool = False
+
+    def __init__(self, collection: WordCollection, reverse: bool = False) -> None:
+        self._collection = collection
+        self._reverse = reverse
+        self._position = -1 if reverse else 0
+
+    def __next__(self):
+        """
+        The __next__() method must return the next item in the sequence. On
+        reaching the end, and in subsequent calls, it must raise StopIteration.
+        """
+
+        try:
+            value = self._collection[self._position]
+            self._position += -1 if self._reverse else 1
+        except IndexError:
+            raise StopIteration()
+
+        return value

behavioral/iterator/main.py

@@ -0,0 +1,17 @@
+"""
+The client code may or may not know about the Concrete Iterator or Collection
+classes, depending on the level of indirection you want to keep in your program.
+"""
+from behavioral.iterator.alpha_order_iterator import WordCollection
+
+collection = WordCollection()
+collection.add_item("First")
+collection.add_item("Second")
+collection.add_item("Third")
+
+print("Straight traversal:")
+print("\n".join(collection))
+print("")
+
+print("Reverse traversal:")
+print("\n".join(collection.get_reverse_iterator()), end="")