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ch11: sample code
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‎11-pythonic-obj/README.md

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

‎11-pythonic-obj/mem_test.py

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

‎11-pythonic-obj/private/Confidential.java

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public class Confidential {
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private String secret = "";
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public Confidential(String text) {
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secret = text.toUpperCase();
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}
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}

‎11-pythonic-obj/private/Expose.java

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

‎11-pythonic-obj/private/expose.py

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import Confidential
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message = Confidential('top secret text')
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secret_field = Confidential.getDeclaredField('secret')
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secret_field.setAccessible(True) # break the lock!
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print 'message.secret =', secret_field.get(message)

‎11-pythonic-obj/private/leakprivate.py

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

‎11-pythonic-obj/private/no_respect.py

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

‎11-pythonic-obj/vector2d_v0.py

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

‎11-pythonic-obj/vector2d_v1.py

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

‎11-pythonic-obj/vector2d_v2.py

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

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