last example of chapter 9: classes/vector_v5.py

classes/vector2d_v1.py

@@ -0,0 +1,85 @@
+"""
+A 2-dimensional vector class
+
+    >>> v1 = Vector2d(3, 4)
+    >>> x, y = v1  #<1>
+    >>> x, y
+    (3.0, 4.0)
+    >>> v1  #<2>
+    Vector2d(3.0, 4.0)
+    >>> v1_clone = eval(repr(v1))  #<3>
+    >>> v1 == v1_clone
+    True
+    >>> print(v1)  #<4>
+    (3.0, 4.0)
+    >>> octets = bytes(v1)  #<5>
+    >>> octets
+    b'\\x00\\x00\\x00\\x00\\x00\\x00\\x08@\\x00\\x00\\x00\\x00\\x00\\x00\\x10@'
+    >>> abs(v1)  #<6>
+    5.0
+    >>> bool(v1), bool(Vector2d(0, 0))  #<7>
+    (True, False)
+
+Test of .frombytes() class method:
+
+    >>> v1_clone = Vector2d.frombytes(bytes(v1))
+    >>> v1_clone
+    Vector2d(3.0, 4.0)
+    >>> v1 == v1_clone
+    True
+
+So far, Vector2d instances are unhashable:
+
+# BEGIN VECTOR2D_V1_UNHASHABLE_DEMO
+    >>> v1 = Vector2d(3, 4)
+    >>> hash(v1)
+    Traceback (most recent call last):
+      ...
+    TypeError: unhashable type: 'Vector2d'
+    >>> set([v1])
+    Traceback (most recent call last):
+      ...
+    TypeError: unhashable type: 'Vector2d'
+
+# END VECTOR2D_V1_UNHASHABLE_DEMO
+
+"""
+
+from array import array
+import math
+
+
+class Vector2d:
+    typecode = 'd'
+
+    def __init__(self, x, y):
+        self.x = float(x)
+        self.y = float(y)
+
+    def __iter__(self):
+        return (i for i in (self.x, self.y))
+
+    def __repr__(self):
+        return 'Vector2d({!r}, {!r})'.format(*self)
+
+    def __str__(self):
+        return str(tuple(self))
+
+    def __bytes__(self):
+        return bytes(array(Vector2d.typecode, self))
+
+    def __eq__(self, other):
+        return tuple(self) == tuple(other)
+
+    def __abs__(self):
+        return math.hypot(self.x, self.y)
+
+    def __bool__(self):
+        return bool(abs(self))
+
+# BEGIN VECTOR2D_V1
+    @classmethod  # <1>
+    def frombytes(cls, octets):  # <2>
+        memv = memoryview(octets).cast(cls.typecode)  # <3>
+        return cls(*memv)  # <4>
+# END VECTOR2D_V1