ch06: update from book draft

06-obj-ref/README.rst

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+Sample code for Chapter 8 - "Object references, mutability and recycling"
+
+From the book "Fluent Python" by Luciano Ramalho (O'Reilly, 2015)
+http://shop.oreilly.com/product/0636920032519.do

06-obj-ref/bus.py

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+
+"""
+>>> import copy
+>>> bus1 = Bus(['Alice', 'Bill', 'Claire', 'David'])
+>>> bus2 = copy.copy(bus1)
+>>> bus3 = copy.deepcopy(bus1)
+>>> bus1.drop('Bill')
+>>> bus2.passengers
+['Alice', 'Claire', 'David']
+>>> bus3.passengers
+['Alice', 'Bill', 'Claire', 'David']
+
+"""
+
+# tag::BUS_CLASS[]
+class Bus:
+
+    def __init__(self, passengers=None):
+        if passengers is None:
+            self.passengers = []
+        else:
+            self.passengers = list(passengers)
+
+    def pick(self, name):
+        self.passengers.append(name)
+
+    def drop(self, name):
+        self.passengers.remove(name)
+# end::BUS_CLASS[]

06-obj-ref/cheese.py

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+"""
+>>> import weakref
+>>> stock = weakref.WeakValueDictionary()
+>>> catalog = [Cheese('Red Leicester'), Cheese('Tilsit'),
+...                 Cheese('Brie'), Cheese('Parmesan')]
+...
+>>> for cheese in catalog:
+...     stock[cheese.kind] = cheese
+...
+>>> sorted(stock.keys())
+['Brie', 'Parmesan', 'Red Leicester', 'Tilsit']
+>>> del catalog
+>>> sorted(stock.keys())
+['Parmesan']
+>>> del cheese
+>>> sorted(stock.keys())
+[]
+"""
+
+# tag::CHEESE_CLASS[]
+class Cheese:
+
+    def __init__(self, kind):
+        self.kind = kind
+
+    def __repr__(self):
+        return 'Cheese(%r)' % self.kind
+# end::CHEESE_CLASS[]

06-obj-ref/haunted_bus.py

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+"""
+>>> bus1 = HauntedBus(['Alice', 'Bill'])
+>>> bus1.passengers
+['Alice', 'Bill']
+>>> bus1.pick('Charlie')
+>>> bus1.drop('Alice')
+>>> bus1.passengers
+['Bill', 'Charlie']
+>>> bus2 = HauntedBus()
+>>> bus2.pick('Carrie')
+>>> bus2.passengers
+['Carrie']
+>>> bus3 = HauntedBus()
+>>> bus3.passengers
+['Carrie']
+>>> bus3.pick('Dave')
+>>> bus2.passengers
+['Carrie', 'Dave']
+>>> bus2.passengers is bus3.passengers
+True
+>>> bus1.passengers
+['Bill', 'Charlie']
+
+
+>>> dir(HauntedBus.__init__)  # doctest: +ELLIPSIS
+['__annotations__', '__call__', ..., '__defaults__', ...]
+>>> HauntedBus.__init__.__defaults__
+(['Carrie', 'Dave'],)
+>>> HauntedBus.__init__.__defaults__[0] is bus2.passengers
+True
+
+"""
+
+# tag::HAUNTED_BUS_CLASS[]
+class HauntedBus:
+    """A bus model haunted by ghost passengers"""
+
+    def __init__(self, passengers=[]):  # <1>
+        self.passengers = passengers  # <2>
+
+    def pick(self, name):
+        self.passengers.append(name)  # <3>
+
+    def drop(self, name):
+        self.passengers.remove(name)
+# end::HAUNTED_BUS_CLASS[]
+

06-obj-ref/twilight_bus.py

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+"""
+>>> basketball_team = ['Sue', 'Tina', 'Maya', 'Diana', 'Pat']
+>>> bus = TwilightBus(basketball_team)
+>>> bus.drop('Tina')
+>>> bus.drop('Pat')
+>>> basketball_team
+['Sue', 'Maya', 'Diana']
+"""
+
+# tag::TWILIGHT_BUS_CLASS[]
+class TwilightBus:
+    """A bus model that makes passengers vanish"""
+
+    def __init__(self, passengers=None):
+        if passengers is None:
+            self.passengers = []  # <1>
+        else:
+            self.passengers = passengers  #<2>
+
+    def pick(self, name):
+        self.passengers.append(name)
+
+    def drop(self, name):
+        self.passengers.remove(name)  # <3>
+# end::TWILIGHT_BUS_CLASS[]
+