Ejercicio 15b

exercises/ex15/queue.py

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+class QueueNode(object):
+    def __init__(self, value, prev, 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.next
+        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 == self.end:
+                self.begin = self.end = None
+            else:
+                self.begin = self.begin.next
+                self.begin.prev = 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(obj, None, self.begin)
+        if self.begin is None:
+            self.begin = node
+            self.end = self.begin
+        else:
+            self.begin.prev = node
+            self.begin = node
+
+    def top(self):
+        """
+        Returns value of first item.
+        Regresa el valor del primer ítem.
+        """
+        return self.begin.value
+
+    def bottom(self):
+        """
+        Returns value of last item.
+        Regresa el valor del último ítem.
+        """
+        return self.end.value

exercises/ex15/test_queue.py

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+from queue import Queue
+
+
+def test_unshift():
+    colors = Queue()
+    colors.shift("Viridian")
+    colors.shift("Sap Green")
+    colors.shift("Van Dyke")
+    assert colors.unshift() == "Van Dyke"
+    assert colors.unshift() == "Sap Green"
+    assert colors.unshift() == "Viridian"
+    assert colors.unshift() is None
+    assert colors.count() == 0
+
+
+def test_shift():
+    colors = Queue()
+    colors.shift("Cadmium Orange")
+    assert colors.count() == 1
+    colors.shift("Carbazole Violet")
+    assert colors.count() == 2
+    assert colors.unshift() == "Carbazole Violet"
+    assert colors.count() == 1
+    assert colors.unshift() == "Cadmium Orange"
+    assert colors.count() == 0
+
+
+def test_top():
+    colors = Queue()
+    colors.shift("Cadmium Red Light")
+    assert colors.top() == "Cadmium Red Light"
+    colors.shift("Hansa Yellow")
+    assert colors.top() == "Hansa Yellow"
+    colors.shift("Pthalo Green")
+    assert colors.top() == "Pthalo Green"
+
+
+def test_bottom():
+    colors = Queue()
+    colors.shift("Cadmium Red Light")
+    assert colors.bottom() == "Cadmium Red Light"
+    colors.shift("Hansa Yellow")
+    assert colors.bottom() == "Cadmium Red Light"
+    colors.shift("Pthalo Green")
+    assert colors.bottom() == "Cadmium Red Light"