ch11: sample code

11-pythonic-obj/README.md

@@ -0,0 +1,3 @@
+# The Python Data Model
+
+Sample code for Chapter 11 of _Fluent Python 2e_ by Luciano Ramalho (O'Reilly, 2020)

11-pythonic-obj/mem_test.py

@@ -0,0 +1,24 @@
+import importlib
+import sys
+import resource
+
+NUM_VECTORS = 10**7
+
+if len(sys.argv) == 2:
+    module_name = sys.argv[1].replace('.py', '')
+    module = importlib.import_module(module_name)
+else:
+    print('Usage: {} <vector-module-to-test>'.format())
+    sys.exit(1)
+
+fmt = 'Selected Vector2d type: {.__name__}.{.__name__}'
+print(fmt.format(module, module.Vector2d))
+
+mem_init = resource.getrusage(resource.RUSAGE_SELF).ru_maxrss
+print('Creating {:,} Vector2d instances'.format(NUM_VECTORS))
+
+vectors = [module.Vector2d(3.0, 4.0) for i in range(NUM_VECTORS)]
+
+mem_final = resource.getrusage(resource.RUSAGE_SELF).ru_maxrss
+print('Initial RAM usage: {:14,}'.format(mem_init))
+print('  Final RAM usage: {:14,}'.format(mem_final))

11-pythonic-obj/private/Confidential.java

@@ -0,0 +1,8 @@
+public class Confidential {
+
+    private String secret = "";
+
+    public Confidential(String text) {
+        secret = text.toUpperCase();
+    }
+}

11-pythonic-obj/private/Expose.java

@@ -0,0 +1,25 @@
+import java.lang.reflect.Field;
+
+public class Expose {
+
+    public static void main(String[] args) {
+        Confidential message = new Confidential("top secret text");
+        Field secretField = null;
+        try {
+            secretField = Confidential.class.getDeclaredField("secret");
+        }
+        catch (NoSuchFieldException e) {
+            System.err.println(e);
+            System.exit(1);
+        }
+        secretField.setAccessible(true); // break the lock!
+        try {
+            String wasHidden = (String) secretField.get(message);
+            System.out.println("message.secret = " + wasHidden);
+        }
+        catch (IllegalAccessException e) { 
+            // this will not happen after setAcessible(true)
+            System.err.println(e);
+        }   
+    }
+}

11-pythonic-obj/private/expose.py

@@ -0,0 +1,6 @@
+import Confidential
+
+message = Confidential('top secret text')
+secret_field = Confidential.getDeclaredField('secret')
+secret_field.setAccessible(True)  # break the lock!
+print 'message.secret =', secret_field.get(message)

11-pythonic-obj/private/leakprivate.py

@@ -0,0 +1,11 @@
+from java.lang.reflect import Modifier
+import Confidential
+
+message = Confidential('top secret text')
+fields = Confidential.getDeclaredFields()
+for field in fields:
+    # list private fields only
+    if Modifier.isPrivate(field.getModifiers()):
+        field.setAccessible(True) # break the lock
+        print 'field:', field
+        print '\t', field.getName(), '=', field.get(message)

11-pythonic-obj/private/no_respect.py

@@ -0,0 +1,17 @@
+
+"""
+In the Jython registry file there is this line:
+
+python.security.respectJavaAccessibility = true
+
+Set this to false and Jython provides access to non-public
+fields, methods, and constructors of Java objects.
+"""
+
+import Confidential
+
+message = Confidential('top secret text')
+for name in dir(message):
+    attr = getattr(message, name)
+    if not callable(attr):  # non-methods only
+        print name + '\t=', attr

11-pythonic-obj/vector2d_v0.py

@@ -0,0 +1,64 @@
+"""
+A 2-dimensional vector class
+
+# tag::VECTOR2D_V0_DEMO[]
+
+    >>> v1 = Vector2d(3, 4)
+    >>> print(v1.x, v1.y)  # <1>
+    3.0 4.0
+    >>> x, y = v1  # <2>
+    >>> x, y
+    (3.0, 4.0)
+    >>> v1  # <3>
+    Vector2d(3.0, 4.0)
+    >>> v1_clone = eval(repr(v1))  # <4>
+    >>> v1 == v1_clone  # <5>
+    True
+    >>> print(v1)  # <6>
+    (3.0, 4.0)
+    >>> octets = bytes(v1)  # <7>
+    >>> octets
+    b'd\\x00\\x00\\x00\\x00\\x00\\x00\\x08@\\x00\\x00\\x00\\x00\\x00\\x00\\x10@'
+    >>> abs(v1)  # <8>
+    5.0
+    >>> bool(v1), bool(Vector2d(0, 0))  # <9>
+    (True, False)
+
+# end::VECTOR2D_V0_DEMO[]
+"""
+
+# tag::VECTOR2D_V0[]
+from array import array
+import math
+
+
+class Vector2d:
+    typecode = 'd'  # <1>
+
+    def __init__(self, x, y):
+        self.x = float(x)    # <2>
+        self.y = float(y)
+
+    def __iter__(self):
+        return (i for i in (self.x, self.y))  # <3>
+
+    def __repr__(self):
+        class_name = type(self).__name__
+        return '{}({!r}, {!r})'.format(class_name, *self)  # <4>
+
+    def __str__(self):
+        return str(tuple(self))  # <5>
+
+    def __bytes__(self):
+        return (bytes([ord(self.typecode)]) +  # <6>
+                bytes(array(self.typecode, self)))  # <7>
+
+    def __eq__(self, other):
+        return tuple(self) == tuple(other)  # <8>
+
+    def __abs__(self):
+        return math.hypot(self.x, self.y)  # <9>
+
+    def __bool__(self):
+        return bool(abs(self))  # <10>
+# end::VECTOR2D_V0[]

11-pythonic-obj/vector2d_v1.py

@@ -0,0 +1,76 @@
+"""
+A 2-dimensional vector class
+
+    >>> v1 = Vector2d(3, 4)
+    >>> print(v1.x, v1.y)
+    3.0 4.0
+    >>> x, y = v1
+    >>> x, y
+    (3.0, 4.0)
+    >>> v1
+    Vector2d(3.0, 4.0)
+    >>> v1_clone = eval(repr(v1))
+    >>> v1 == v1_clone
+    True
+    >>> print(v1)
+    (3.0, 4.0)
+    >>> octets = bytes(v1)
+    >>> octets
+    b'd\\x00\\x00\\x00\\x00\\x00\\x00\\x08@\\x00\\x00\\x00\\x00\\x00\\x00\\x10@'
+    >>> abs(v1)
+    5.0
+    >>> bool(v1), bool(Vector2d(0, 0))
+    (True, False)
+
+
+Test of ``.frombytes()`` class method:
+
+    >>> v1_clone = Vector2d.frombytes(bytes(v1))
+    >>> v1_clone
+    Vector2d(3.0, 4.0)
+    >>> v1 == v1_clone
+    True
+
+"""
+
+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):
+        class_name = type(self).__name__
+        return '{}({!r}, {!r})'.format(class_name, *self)
+
+    def __str__(self):
+        return str(tuple(self))
+
+    def __bytes__(self):
+        return (bytes([ord(self.typecode)]) +
+                bytes(array(self.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))
+
+# tag::VECTOR2D_V1[]
+    @classmethod  # <1>
+    def frombytes(cls, octets):  # <2>
+        typecode = chr(octets[0])  # <3>
+        memv = memoryview(octets[1:]).cast(typecode)  # <4>
+        return cls(*memv)  # <5>
+# end::VECTOR2D_V1[]

11-pythonic-obj/vector2d_v2.py

@@ -0,0 +1,123 @@
+"""
+A 2-dimensional vector class
+
+    >>> v1 = Vector2d(3, 4)
+    >>> print(v1.x, v1.y)
+    3.0 4.0
+    >>> x, y = v1
+    >>> x, y
+    (3.0, 4.0)
+    >>> v1
+    Vector2d(3.0, 4.0)
+    >>> v1_clone = eval(repr(v1))
+    >>> v1 == v1_clone
+    True
+    >>> print(v1)
+    (3.0, 4.0)
+    >>> octets = bytes(v1)
+    >>> octets
+    b'd\\x00\\x00\\x00\\x00\\x00\\x00\\x08@\\x00\\x00\\x00\\x00\\x00\\x00\\x10@'
+    >>> abs(v1)
+    5.0
+    >>> bool(v1), bool(Vector2d(0, 0))
+    (True, False)
+
+
+Test of ``.frombytes()`` class method:
+
+    >>> v1_clone = Vector2d.frombytes(bytes(v1))
+    >>> v1_clone
+    Vector2d(3.0, 4.0)
+    >>> v1 == v1_clone
+    True
+
+
+Tests of ``format()`` with Cartesian coordinates:
+
+    >>> format(v1)
+    '(3.0, 4.0)'
+    >>> format(v1, '.2f')
+    '(3.00, 4.00)'
+    >>> format(v1, '.3e')
+    '(3.000e+00, 4.000e+00)'
+
+
+Tests of the ``angle`` method::
+
+    >>> Vector2d(0, 0).angle()
+    0.0
+    >>> Vector2d(1, 0).angle()
+    0.0
+    >>> epsilon = 10**-8
+    >>> abs(Vector2d(0, 1).angle() - math.pi/2) < epsilon
+    True
+    >>> abs(Vector2d(1, 1).angle() - math.pi/4) < epsilon
+    True
+
+
+Tests of ``format()`` with polar coordinates:
+
+    >>> format(Vector2d(1, 1), 'p')  # doctest:+ELLIPSIS
+    '<1.414213..., 0.785398...>'
+    >>> format(Vector2d(1, 1), '.3ep')
+    '<1.414e+00, 7.854e-01>'
+    >>> format(Vector2d(1, 1), '0.5fp')
+    '<1.41421, 0.78540>'
+
+"""
+
+# BEGIN VECTOR2D_V2
+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):
+        class_name = type(self).__name__
+        return '{}({!r}, {!r})'.format(class_name, *self)
+
+    def __str__(self):
+        return str(tuple(self))
+
+    def __bytes__(self):
+        return (bytes([ord(self.typecode)]) +
+                bytes(array(self.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))
+
+    def angle(self):
+        return math.atan2(self.y, self.x)
+
+    def __format__(self, fmt_spec=''):
+        if fmt_spec.endswith('p'):
+            fmt_spec = fmt_spec[:-1]
+            coords = (abs(self), self.angle())
+            outer_fmt = '<{}, {}>'
+        else:
+            coords = self
+            outer_fmt = '({}, {})'
+        components = (format(c, fmt_spec) for c in coords)
+        return outer_fmt.format(*components)
+
+    @classmethod
+    def frombytes(cls, octets):
+        typecode = chr(octets[0])
+        memv = memoryview(octets[1:]).cast(typecode)
+        return cls(*memv)
+# END VECTOR2D_V2

11-pythonic-obj/vector2d_v2_fmt_snippet.py

@@ -0,0 +1,119 @@
+"""
+A 2-dimensional vector class
+
+    >>> v1 = Vector2d(3, 4)
+    >>> x, y = v1
+    >>> x, y
+    (3.0, 4.0)
+    >>> v1
+    Vector2d(3.0, 4.0)
+    >>> v1_clone = eval(repr(v1))
+    >>> v1 == v1_clone
+    True
+    >>> print(v1)
+    (3.0, 4.0)
+    >>> octets = bytes(v1)
+    >>> octets
+    b'\\x00\\x00\\x00\\x00\\x00\\x00\\x08@\\x00\\x00\\x00\\x00\\x00\\x00\\x10@'
+    >>> abs(v1)
+    5.0
+    >>> bool(v1), bool(Vector2d(0, 0))
+    (True, False)
+
+
+Test of ``.frombytes()`` class method:
+
+    >>> v1_clone = Vector2d.frombytes(bytes(v1))
+    >>> v1_clone
+    Vector2d(3.0, 4.0)
+    >>> v1 == v1_clone
+    True
+
+
+Tests of ``format()`` with Cartesian coordinates:
+
+    >>> format(v1)
+    '(3.0, 4.0)'
+    >>> format(v1, '.2f')
+    '(3.00, 4.00)'
+    >>> format(v1, '.3e')
+    '(3.000e+00, 4.000e+00)'
+
+
+Tests of the ``angle`` method::
+
+    >>> Vector2d(0, 0).angle()
+    0.0
+    >>> Vector2d(1, 0).angle()
+    0.0
+    >>> epsilon = 10**-8
+    >>> abs(Vector2d(0, 1).angle() - math.pi/2) < epsilon
+    True
+    >>> abs(Vector2d(1, 1).angle() - math.pi/4) < epsilon
+    True
+
+
+Tests of ``format()`` with polar coordinates:
+
+    >>> format(Vector2d(1, 1), 'p')  # doctest:+ELLIPSIS
+    '<1.414213..., 0.785398...>'
+    >>> format(Vector2d(1, 1), '.3ep')
+    '<1.414e+00, 7.854e-01>'
+    >>> format(Vector2d(1, 1), '0.5fp')
+    '<1.41421, 0.78540>'
+
+"""
+
+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):
+        class_name = type(self).__name__
+        return '{}({!r}, {!r})'.format(class_name, *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))
+
+    def angle(self):
+        return math.atan2(self.y, self.x)
+
+# tag::VECTOR2D_V2_FORMAT[]
+    def __format__(self, fmt_spec=''):
+        if fmt_spec.endswith('p'):  # <1>
+            fmt_spec = fmt_spec[:-1]  # <2>
+            coords = (abs(self), self.angle())  # <3>
+            outer_fmt = '<{}, {}>'  # <4>
+        else:
+            coords = self  # <5>
+            outer_fmt = '({}, {})'  # <6>
+        components = (format(c, fmt_spec) for c in coords)  # <7>
+        return outer_fmt.format(*components)  # <8>
+# end::VECTOR2D_V2_FORMAT[]
+
+    @classmethod
+    def frombytes(cls, octets):
+        memv = memoryview(octets).cast(cls.typecode)
+        return cls(*memv)

11-pythonic-obj/vector2d_v3.py

@@ -0,0 +1,151 @@
+"""
+A two-dimensional vector class
+
+    >>> v1 = Vector2d(3, 4)
+    >>> print(v1.x, v1.y)
+    3.0 4.0
+    >>> x, y = v1
+    >>> x, y
+    (3.0, 4.0)
+    >>> v1
+    Vector2d(3.0, 4.0)
+    >>> v1_clone = eval(repr(v1))
+    >>> v1 == v1_clone
+    True
+    >>> print(v1)
+    (3.0, 4.0)
+    >>> octets = bytes(v1)
+    >>> octets
+    b'd\\x00\\x00\\x00\\x00\\x00\\x00\\x08@\\x00\\x00\\x00\\x00\\x00\\x00\\x10@'
+    >>> abs(v1)
+    5.0
+    >>> bool(v1), bool(Vector2d(0, 0))
+    (True, False)
+
+
+Test of ``.frombytes()`` class method:
+
+    >>> v1_clone = Vector2d.frombytes(bytes(v1))
+    >>> v1_clone
+    Vector2d(3.0, 4.0)
+    >>> v1 == v1_clone
+    True
+
+
+Tests of ``format()`` with Cartesian coordinates:
+
+    >>> format(v1)
+    '(3.0, 4.0)'
+    >>> format(v1, '.2f')
+    '(3.00, 4.00)'
+    >>> format(v1, '.3e')
+    '(3.000e+00, 4.000e+00)'
+
+
+Tests of the ``angle`` method::
+
+    >>> Vector2d(0, 0).angle()
+    0.0
+    >>> Vector2d(1, 0).angle()
+    0.0
+    >>> epsilon = 10**-8
+    >>> abs(Vector2d(0, 1).angle() - math.pi/2) < epsilon
+    True
+    >>> abs(Vector2d(1, 1).angle() - math.pi/4) < epsilon
+    True
+
+
+Tests of ``format()`` with polar coordinates:
+
+    >>> format(Vector2d(1, 1), 'p')  # doctest:+ELLIPSIS
+    '<1.414213..., 0.785398...>'
+    >>> format(Vector2d(1, 1), '.3ep')
+    '<1.414e+00, 7.854e-01>'
+    >>> format(Vector2d(1, 1), '0.5fp')
+    '<1.41421, 0.78540>'
+
+
+Tests of `x` and `y` read-only properties:
+
+    >>> v1.x, v1.y
+    (3.0, 4.0)
+    >>> v1.x = 123
+    Traceback (most recent call last):
+      ...
+    AttributeError: can't set attribute
+
+
+Tests of hashing:
+
+    >>> v1 = Vector2d(3, 4)
+    >>> v2 = Vector2d(3.1, 4.2)
+    >>> hash(v1), hash(v2)
+    (7, 384307168202284039)
+    >>> len(set([v1, v2]))
+    2
+
+"""
+
+from array import array
+import math
+
+class Vector2d:
+    typecode = 'd'
+
+    def __init__(self, x, y):
+        self.__x = float(x)
+        self.__y = float(y)
+
+    @property
+    def x(self):
+        return self.__x
+
+    @property
+    def y(self):
+        return self.__y
+
+    def __iter__(self):
+        return (i for i in (self.x, self.y))
+
+    def __repr__(self):
+        class_name = type(self).__name__
+        return '{}({!r}, {!r})'.format(class_name, *self)
+
+    def __str__(self):
+        return str(tuple(self))
+
+    def __bytes__(self):
+        return (bytes([ord(self.typecode)]) +
+                bytes(array(self.typecode, self)))
+
+    def __eq__(self, other):
+        return tuple(self) == tuple(other)
+
+    def __hash__(self):
+        return hash(self.x) ^ hash(self.y)
+
+    def __abs__(self):
+        return math.hypot(self.x, self.y)
+
+    def __bool__(self):
+        return bool(abs(self))
+
+    def angle(self):
+        return math.atan2(self.y, self.x)
+
+    def __format__(self, fmt_spec=''):
+        if fmt_spec.endswith('p'):
+            fmt_spec = fmt_spec[:-1]
+            coords = (abs(self), self.angle())
+            outer_fmt = '<{}, {}>'
+        else:
+            coords = self
+            outer_fmt = '({}, {})'
+        components = (format(c, fmt_spec) for c in coords)
+        return outer_fmt.format(*components)
+
+    @classmethod
+    def frombytes(cls, octets):
+        typecode = chr(octets[0])
+        memv = memoryview(octets[1:]).cast(typecode)
+        return cls(*memv)

11-pythonic-obj/vector2d_v3_prophash.py

@@ -0,0 +1,161 @@
+"""
+A 2-dimensional vector class
+
+    >>> v1 = Vector2d(3, 4)
+    >>> print(v1.x, v1.y)
+    3.0 4.0
+    >>> x, y = v1
+    >>> x, y
+    (3.0, 4.0)
+    >>> v1
+    Vector2d(3.0, 4.0)
+    >>> v1_clone = eval(repr(v1))
+    >>> v1 == v1_clone
+    True
+    >>> print(v1)
+    (3.0, 4.0)
+    >>> octets = bytes(v1)
+    >>> octets
+    b'd\\x00\\x00\\x00\\x00\\x00\\x00\\x08@\\x00\\x00\\x00\\x00\\x00\\x00\\x10@'
+    >>> abs(v1)
+    5.0
+    >>> bool(v1), bool(Vector2d(0, 0))
+    (True, False)
+
+
+Test of ``.frombytes()`` class method:
+
+    >>> v1_clone = Vector2d.frombytes(bytes(v1))
+    >>> v1_clone
+    Vector2d(3.0, 4.0)
+    >>> v1 == v1_clone
+    True
+
+
+Tests of ``format()`` with Cartesian coordinates:
+
+    >>> format(v1)
+    '(3.0, 4.0)'
+    >>> format(v1, '.2f')
+    '(3.00, 4.00)'
+    >>> format(v1, '.3e')
+    '(3.000e+00, 4.000e+00)'
+
+
+Tests of the ``angle`` method::
+
+    >>> Vector2d(0, 0).angle()
+    0.0
+    >>> Vector2d(1, 0).angle()
+    0.0
+    >>> epsilon = 10**-8
+    >>> abs(Vector2d(0, 1).angle() - math.pi/2) < epsilon
+    True
+    >>> abs(Vector2d(1, 1).angle() - math.pi/4) < epsilon
+    True
+
+
+Tests of ``format()`` with polar coordinates:
+
+    >>> format(Vector2d(1, 1), 'p')  # doctest:+ELLIPSIS
+    '<1.414213..., 0.785398...>'
+    >>> format(Vector2d(1, 1), '.3ep')
+    '<1.414e+00, 7.854e-01>'
+    >>> format(Vector2d(1, 1), '0.5fp')
+    '<1.41421, 0.78540>'
+
+# tag::VECTOR2D_V3_DEMO[]
+Tests of `x` and `y` read-only properties:
+
+    >>> v1.x, v1.y
+    (3.0, 4.0)
+    >>> v1.x = 123
+    Traceback (most recent call last):
+      ...
+    AttributeError: can't set attribute
+
+# end::VECTOR2D_V3_HASH_DEMO[]
+
+Tests of hashing:
+# tag::VECTOR2D_V3_HASH_DEMO[]
+
+    >>> v1 = Vector2d(3, 4)
+    >>> v2 = Vector2d(3.1, 4.2)
+    >>> hash(v1), hash(v2)
+    (7, 384307168202284039)
+    >>> len(set([v1, v2]))
+    2
+
+# end::VECTOR2D_V3_DEMO[]
+
+"""
+
+from array import array
+import math
+
+# tag::VECTOR2D_V3_PROP[]
+class Vector2d:
+    typecode = 'd'
+
+    def __init__(self, x, y):
+        self.__x = float(x)  # <1>
+        self.__y = float(y)
+
+    @property  # <2>
+    def x(self):  # <3>
+        return self.__x  # <4>
+
+    @property  # <5>
+    def y(self):
+        return self.__y
+
+    def __iter__(self):
+        return (i for i in (self.x, self.y))  # <6>
+
+    # remaining methods follow (omitted in book listing)
+# end::VECTOR2D_V3_PROP[]
+
+    def __repr__(self):
+        class_name = type(self).__name__
+        return '{}({!r}, {!r})'.format(class_name, *self)
+
+    def __str__(self):
+        return str(tuple(self))
+
+    def __bytes__(self):
+        return (bytes([ord(self.typecode)]) +
+                bytes(array(self.typecode, self)))
+
+    def __eq__(self, other):
+        return tuple(self) == tuple(other)
+
+# tag::VECTOR_V3_HASH[]
+    def __hash__(self):
+        return hash(self.x) ^ hash(self.y)
+# end::VECTOR_V3_HASH[]
+
+    def __abs__(self):
+        return math.hypot(self.x, self.y)
+
+    def __bool__(self):
+        return bool(abs(self))
+
+    def angle(self):
+        return math.atan2(self.y, self.x)
+
+    def __format__(self, fmt_spec=''):
+        if fmt_spec.endswith('p'):
+            fmt_spec = fmt_spec[:-1]
+            coords = (abs(self), self.angle())
+            outer_fmt = '<{}, {}>'
+        else:
+            coords = self
+            outer_fmt = '({}, {})'
+        components = (format(c, fmt_spec) for c in coords)
+        return outer_fmt.format(*components)
+
+    @classmethod
+    def frombytes(cls, octets):
+        typecode = chr(octets[0])
+        memv = memoryview(octets[1:]).cast(typecode)
+        return cls(*memv)

11-pythonic-obj/vector2d_v3_slots.py

@@ -0,0 +1,158 @@
+"""
+A 2-dimensional vector class
+
+    >>> v1 = Vector2d(3, 4)
+    >>> print(v1.x, v1.y)
+    3.0 4.0
+    >>> x, y = v1
+    >>> x, y
+    (3.0, 4.0)
+    >>> v1
+    Vector2d(3.0, 4.0)
+    >>> v1_clone = eval(repr(v1))
+    >>> v1 == v1_clone
+    True
+    >>> print(v1)
+    (3.0, 4.0)
+    >>> octets = bytes(v1)
+    >>> octets
+    b'd\\x00\\x00\\x00\\x00\\x00\\x00\\x08@\\x00\\x00\\x00\\x00\\x00\\x00\\x10@'
+    >>> abs(v1)
+    5.0
+    >>> bool(v1), bool(Vector2d(0, 0))
+    (True, False)
+
+
+Test of ``.frombytes()`` class method:
+
+    >>> v1_clone = Vector2d.frombytes(bytes(v1))
+    >>> v1_clone
+    Vector2d(3.0, 4.0)
+    >>> v1 == v1_clone
+    True
+
+
+Tests of ``format()`` with Cartesian coordinates:
+
+    >>> format(v1)
+    '(3.0, 4.0)'
+    >>> format(v1, '.2f')
+    '(3.00, 4.00)'
+    >>> format(v1, '.3e')
+    '(3.000e+00, 4.000e+00)'
+
+
+Tests of the ``angle`` method::
+
+    >>> Vector2d(0, 0).angle()
+    0.0
+    >>> Vector2d(1, 0).angle()
+    0.0
+    >>> epsilon = 10**-8
+    >>> abs(Vector2d(0, 1).angle() - math.pi/2) < epsilon
+    True
+    >>> abs(Vector2d(1, 1).angle() - math.pi/4) < epsilon
+    True
+
+
+Tests of ``format()`` with polar coordinates:
+
+    >>> format(Vector2d(1, 1), 'p')  # doctest:+ELLIPSIS
+    '<1.414213..., 0.785398...>'
+    >>> format(Vector2d(1, 1), '.3ep')
+    '<1.414e+00, 7.854e-01>'
+    >>> format(Vector2d(1, 1), '0.5fp')
+    '<1.41421, 0.78540>'
+
+
+Tests of `x` and `y` read-only properties:
+
+    >>> v1.x, v1.y
+    (3.0, 4.0)
+    >>> v1.x = 123
+    Traceback (most recent call last):
+      ...
+    AttributeError: can't set attribute
+
+Tests of hashing:
+
+    >>> v1 = Vector2d(3, 4)
+    >>> v2 = Vector2d(3.1, 4.2)
+    >>> hash(v1), hash(v2)
+    (7, 384307168202284039)
+    >>> len(set([v1, v2]))
+    2
+
+# end::VECTOR2D_V3_DEMO[]
+
+"""
+
+from array import array
+import math
+
+# tag::VECTOR2D_V3_SLOTS[]
+class Vector2d:
+    __slots__ = ('__x', '__y')
+
+    typecode = 'd'
+
+    # methods follow (omitted in book listing)
+# end::VECTOR2D_V3_SLOTS[]
+
+    def __init__(self, x, y):
+        self.__x = float(x)
+        self.__y = float(y)
+
+    @property
+    def x(self):
+        return self.__x
+
+    @property
+    def y(self):
+        return self.__y
+
+    def __iter__(self):
+        return (i for i in (self.x, self.y))
+
+    def __repr__(self):
+        class_name = type(self).__name__
+        return '{}({!r}, {!r})'.format(class_name, *self)
+
+    def __str__(self):
+        return str(tuple(self))
+
+    def __bytes__(self):
+        return (bytes([ord(self.typecode)]) +
+                bytes(array(self.typecode, self)))
+
+    def __eq__(self, other):
+        return tuple(self) == tuple(other)
+
+    def __hash__(self):
+        return hash(self.x) ^ hash(self.y)
+
+    def __abs__(self):
+        return math.hypot(self.x, self.y)
+
+    def __bool__(self):
+        return bool(abs(self))
+
+    def angle(self):
+        return math.atan2(self.y, self.x)
+
+    def __format__(self, fmt_spec=''):
+        if fmt_spec.endswith('p'):
+            fmt_spec = fmt_spec[:-1]
+            coords = (abs(self), self.angle())
+            outer_fmt = '<{}, {}>'
+        else:
+            coords = self
+            outer_fmt = '({}, {})'
+        components = (format(c, fmt_spec) for c in coords)
+        return outer_fmt.format(*components)
+
+    @classmethod
+    def frombytes(cls, octets):
+        typecode = chr(octets[0])
+        memv = memoryview(octets[1:]).cast(typecode)
+        return cls(*memv)