Ejercicios 15a y 15b arreglados

exercises/ex15/queue.py

@@ -0,0 +1,77 @@
+class QueueNode(object):
+    def __init__(self, prev, value, nxt):
+        self.value = value
+        self.next = nxt
+        self.prev = prev
+
+    def __repr__(self):
+        nval = self.next and self.next.value or None
+        pval = self.prev and self.prev.value or None
+        return f"[{repr(pval)}, {self.value}, {repr(nval)}]"
+
+
+class Queue(object):
+    def __init__(self):
+        self.begin = None
+        self.end = None
+
+    def count(self):
+        """
+        Returns number of items.
+        Regresa la cantidad de ítems.
+        """
+        count = 0
+        node = self.begin
+        while node:
+            count += 1
+            node = node.prev
+        return count
+
+    def unshift(self):
+        """
+        Removes the first item and returns its value.
+        Remueve el primer ítem y regresa su valor.
+        """
+        if self.begin is None:
+            value = None
+        else:
+            value = self.begin.value
+            if self.begin.prev is None:
+                self.begin = self.end = None
+            else:
+                self.begin = self.begin.prev
+                self.begin.next = None
+        return value
+
+    def shift(self, obj):
+        """
+        Appends a new item on the begin of the list.
+        Añade un nuevo ítem al inicio de la lista.
+        """
+        node = QueueNode(None, obj, self.begin)
+        if self.begin is None:
+            self.begin = node
+            self.end = self.begin
+        else:
+            self.begin.prev = self.end = node
+
+    def drop(self):
+        """
+        Removes the last item and returns its value.
+        Remueve el último ítem y regresa su valor.
+        """
+        value = self.end and self.end.value or None
+        if value:
+            if self.end.next is None:
+                self.begin = self.end = None
+            else:
+                self.end = self.end.next
+                self.end.prev = None
+        return value
+
+    def first(self):
+        """
+        Returns value of first item.
+        Regresa el valor del primer ítem.
+        """
+        return self.begin and self.begin.value or None

exercises/ex15/test_queue.py

@@ -0,0 +1,40 @@
+from queue import Queue
+
+
+def test_shift():
+    colors = Queue()
+    colors.shift("Pthalo Blue")
+    assert colors.count() == 1
+    colors.shift("Ultramarine Blue")
+    assert colors.count() == 2
+
+
+def test_unshift():
+    colors = Queue()
+    colors.shift("Magenta")
+    colors.shift("Alizarin")
+    assert colors.unshift() == "Magenta"
+    assert colors.unshift() == "Alizarin"
+    assert colors.unshift() is None
+
+
+def test_first():
+    colors = Queue()
+    colors.shift("Cadmium Red Light")
+    assert colors.first() == "Cadmium Red Light"
+    colors.shift("Hansa Yellow")
+    assert colors.first() == "Cadmium Red Light"
+    colors.shift("Pthalo Green")
+    assert colors.first() == "Cadmium Red Light"
+
+
+def test_drop():
+    colors = Queue()
+    colors.shift("Cad Red")
+    colors.shift("Hansa Yellow")
+    assert colors.count() == 2
+    colors.drop()
+    assert colors.count() == 1
+    assert colors.first() == "Cad Red"
+    colors.drop()
+    assert colors.first() is None

exercises/ex15/test_stack.py

@@ -14,9 +14,7 @@ def test_pop():
     colors.push("Magenta")
     colors.push("Alizarin")
     assert colors.pop() == "Alizarin"
-    assert colors.count() == 1
     assert colors.pop() == "Magenta"
-    assert colors.count() == 0
     assert colors.pop() is None
 
 
@@ -26,7 +24,5 @@ def test_top():
     assert colors.top() == "Cadmium Red Light"
     colors.push("Hansa Yellow")
     assert colors.top() == "Hansa Yellow"
-    colors.pop()
-    assert colors.top() == "Cadmium Red Light"
-    colors.pop()
-    assert colors.top() is None
+    colors.push("Pthalo Green")
+    assert colors.top() == "Pthalo Green"