updated oo talk..

Author: PythonCHB

Examples/week-06-OO/constrained_int/readme.rst

@@ -0,0 +1,59 @@
+__new__ example
+---------------
+
+A little excercise for __new__ and making a new class act like a regular type.
+
+Here is a replacement for int which can only take new values between 0 and 255:
+
+::
+
+    class ConstrainedInt(int):
+        def __new__(cls, value):
+            value = value % 256
+            self = int.__new__(cls, value)
+            return self
+
+A reminder of Magic methods:
+-----------------------------
+
+Magic Methods
+
+They all start with and end with '__', and do things like support operators and comparisons, and provide handlers for the object lifecycle.
+
+__cmp__(self, other)
+
+__eq__(self, other)
+
+__add__(self, other)
+
+Also, __call__, __str__, __repr__, __sizeof__,
+__setattr__, __getattr__, __len__, __iter__,
+__contains__, __lshift__, __rshift__, __xor__,
+__div__, __enter__, __exit__,
+
+and my personal favorite __rxor__(self,other)......
+
+The list is really long, it's mostly important to get a flavor of how
+they are used in Python so you can find and implement the right one when
+you need it.
+
+See ``http://www.rafekettler.com/magicmethods.html`` for more
+
+Exercise
+---------
+
+Our ConstrainedInt handles initialization for us, but doesn't handle
+modification of the value
+
+Develop ConstrainedInt until it passes all tests in
+``test_constrained_int.py``
+
+::
+
+    class ConstrainedInt(int):
+        """keeps value between 0 and 255"""
+        def __new__(cls, value):
+            value = value % 256
+            self = int.__new__(cls, value)
+            return self
+

…/constrained_int/constrained_int_test.py …/constrained_int/test_constrained_int.pyExamples/week-06-OO/constrained_int/constrained_int_test.py renamed to Examples/week-06-OO/constrained_int/test_constrained_int.py Examples/week-06-OO/constrained_int/constrained_int_test.py renamed to Examples/week-06-OO/constrained_int/test_constrained_int.py

@@ -0,0 +1,17 @@
+#!/usr/bin/env python
+
+"""
+Using new to create an even integer
+
+rounds the input to the nearest even integer.
+
+will even convert a string to an int...
+
+"""
+
+class EvenInt():
+    """
+    An integer that is always even
+    """
+    pass
+

Examples/week-06-OO/even_int.py

@@ -0,0 +1,20 @@
+#!/usr/bin/env python
+
+"""
+Using new to create an always-positive even integer
+
+rounds the input to the nearest even integer.
+
+will even convert a string to an int...
+
+"""
+
+##subclassing an int
+class EvenInt(int):
+    """
+    An integer that is always even
+    """
+    def __new__(cls, val):
+        val = round(float(val) / 2) * 2
+        return int.__new__(cls, val)
+

Examples/week-06-OO/even_int_solution.py

@@ -1,31 +1,40 @@
 import time
 
+
 class LoggingMixin(object):
     def log(self):
-        print "%s: %s" % (time.time(), self.__repr__())
+        print "%s: %s" % (time.time(), repr(self))
+
 
 class Vehicle(object):
     def log(self):
         print self.__repr__()
 
+
 class TwoWheeledVehicle(Vehicle):
     pass
 
+
 class LightVehicle(Vehicle):
     pass
 
+
 class HeavyVehicle(Vehicle):
     pass
 
+
 class Bike(TwoWheeledVehicle, LightVehicle):
     pass
 
+
 class MotorCycle(TwoWheeledVehicle, HeavyVehicle):
     pass
 
+
 class Tank(HeavyVehicle):
     pass
 
+
 bike = Bike()
 tank = Tank()
 

Examples/week-06-OO/mixins.py

@@ -0,0 +1,40 @@
+#!/usr/bin/env python
+
+"""
+example of __new__
+"""
+
+
+
+## the general case:
+class Test(object):
+    def __new__(cls, arg):
+        print "in __new__", 
+        print arg
+        obj =  object.__new__(cls, arg)
+        obj.this = arg # but you probably don't want to do this!
+        return obj
+
+    def __init__(self, arg):
+        print "in __init__", 
+        print arg
+        self.that = arg
+
+
+##subclassing a string
+
+class CapitalString(str):
+    """
+    A string class that is always capitalized...
+    """
+    def __new__(cls, in_string):
+        print "in CapitalString.__new__"
+        return str.__new__(cls, in_string.title() )
+
+# try it:
+if __name__ == "__main__":
+    print CapitalString("this is a string")
+
+
+
+

Examples/week-06-OO/new_example.py

@@ -0,0 +1,44 @@
+#!/usr/bin/env python
+
+"""
+tests for an even integer class
+"""
+
+from even_int import EvenInt
+#from even_int_solution import EvenInt
+
+## And some tests -- try with py.test or nosetests...
+def test_subclass():
+    assert issubclass(EvenInt, int)
+
+def test_instance():
+    i = EvenInt(3)
+    assert isinstance(i, int)
+
+def test_even():
+    assert EvenInt(4) == 4
+
+def test_odd1():
+    assert EvenInt(3) == 4
+
+def test_odd2():
+    assert EvenInt(2.99) == 2
+
+def test_negative():
+    assert EvenInt(-2) == -2
+
+def test_negative_odd():
+    assert EvenInt(-1) == -2
+
+def test_negative_odd2():
+    assert EvenInt(-1.1) == -2
+
+def test_string_odd():
+    assert EvenInt("3") == 4
+
+def test_string_even():
+    assert EvenInt("12") == 12
+
+def test_string_float():
+    assert EvenInt("4.45") == 4
+