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#!/usr/bin/env PYTHONHASHSEED=1234 python3
# Copyright 2014-2019 Brett Slatkin, Pearson Education Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# Reproduce book environment
import random
random.seed(1234)
import logging
from pprint import pprint
from sys import stdout as STDOUT
# Write all output to a temporary directory
import atexit
import gc
import io
import os
import tempfile
TEST_DIR = tempfile.TemporaryDirectory()
atexit.register(TEST_DIR.cleanup)
# Make sure Windows processes exit cleanly
OLD_CWD = os.getcwd()
atexit.register(lambda: os.chdir(OLD_CWD))
os.chdir(TEST_DIR.name)
def close_open_files():
everything = gc.get_objects()
for obj in everything:
if isinstance(obj, io.IOBase):
obj.close()
atexit.register(close_open_files)
# Example 1
class MyBaseClass:
def __init__(self, value):
self.value = value
class MyChildClass(MyBaseClass):
def __init__(self):#gets value from parents class
MyBaseClass.__init__(self, 5)#add value to var in parent class
def times_two(self):
return self.value * 2
foo = MyChildClass()
assert foo.times_two() == 10
print(foo.times_two())#10
# Example 2
class TimesTwo:
def __init__(self):
self.value *= 2
class PlusFive:
def __init__(self):
self.value += 5
# Example 3
class OneWay(MyBaseClass, TimesTwo, PlusFive):#class with link to other classes
def __init__(self, value):
MyBaseClass.__init__(self, value)#orig class with link to parent
TimesTwo.__init__(self)#independent class
PlusFive.__init__(self)#independent class
# Example 4
foo = OneWay(5)#call overview class
print('First ordering value is (5 * 2) + 5 =', foo.value)#init value from orig class used with different methods
# Example 5
class AnotherWay(MyBaseClass, PlusFive, TimesTwo):#overview class link to other classes
def __init__(self, value):
MyBaseClass.__init__(self, value)
TimesTwo.__init__(self)
PlusFive.__init__(self)
# Example 6
bar = AnotherWay(5)#call overview class as new class order args not relevant for result
print('Second ordering value is', bar.value)
# Example 7
class TimesSeven(MyBaseClass):#class with link to parent
def __init__(self, value):
MyBaseClass.__init__(self, value)
self.value *= 7
class PlusNine(MyBaseClass):#class with link to parent
def __init__(self, value):
MyBaseClass.__init__(self, value)
self.value += 9
# Example 8
class ThisWay(TimesSeven, PlusNine):#overview class with link to classes
def __init__(self, value):
TimesSeven.__init__(self, value)
PlusNine.__init__(self, value)
a=TimesSeven(5)
print(a.value)#35
b=PlusNine(5)
print(b.value)#14
foo = ThisWay(5)
print('Should be (5 * 7) + 9 = 44 but is', foo.value)#Should be (5 * 7) + 9 = 44 but is 14 => var seems to be overwritten
# Example 9
class MyBaseClass:
def __init__(self, value):
self.value = value
class TimesSevenCorrect(MyBaseClass):#first in stack last executed
def __init__(self, value):
super().__init__(value)
self.value *= 7
class PlusNineCorrect(MyBaseClass):#second in stack lifo system so first add then multiply
def __init__(self, value):
super().__init__(value)
self.value += 9
# Example 10
class GoodWay(TimesSevenCorrect, PlusNineCorrect):
def __init__(self, value):
super().__init__(value)
foo = GoodWay(5)
print('Should be 7 * (5 + 9) = 98 and is', foo.value)#Should be 7 * (5 + 9) = 98 and is 98
# Example 11
mro_str = '\n'.join(repr(cls) for cls in GoodWay.mro())#Return a type's method resolution order.
print(mro_str)
#<class '__main__.GoodWay'>
#<class '__main__.TimesSevenCorrect'>
#<class '__main__.PlusNineCorrect'>
#<class '__main__.MyBaseClass'>
#<class 'object'>
# Example 12
class ExplicitTrisect(MyBaseClass):
def __init__(self, value):
super(ExplicitTrisect, self).__init__(value)#detailed call of super even same class
self.value /= 3
assert ExplicitTrisect(9).value == 3
# Example 13
class AutomaticTrisect(MyBaseClass):
def __init__(self, value):
super(__class__, self).__init__(value)#detailed call of super even same class
self.value /= 3
class ImplicitTrisect(MyBaseClass):
def __init__(self, value):
super().__init__(value)#standaard call of super
self.value /= 3
assert ExplicitTrisect(9).value == 3
assert AutomaticTrisect(9).value == 3
assert ImplicitTrisect(9).value == 3