effectivepython/example_code/item_27.py at master · AISTLAB/effectivepython · GitHub

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#!/usr/bin/env python3

# 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.

# Preamble to mimick book environment

import logging

from pprint import pprint

from sys import stdout as STDOUT

# Example 1

class MyObject(object):

def __init__(self):

self.public_field = 5

self.__private_field = 10

def get_private_field(self):

return self.__private_field

# Example 2

foo = MyObject()

assert foo.public_field == 5

# Example 3

assert foo.get_private_field() == 10

# Example 4

try:

foo.__private_field

except:

logging.exception('Expected')

else:

assert False

# Example 5

class MyOtherObject(object):

def __init__(self):

self.__private_field = 71

@classmethod

def get_private_field_of_instance(cls, instance):

return instance.__private_field

bar = MyOtherObject()

assert MyOtherObject.get_private_field_of_instance(bar) == 71

# Example 6

try:

class MyParentObject(object):

def __init__(self):

self.__private_field = 71

class MyChildObject(MyParentObject):

def get_private_field(self):

return self.__private_field

baz = MyChildObject()

baz.get_private_field()

except:

logging.exception('Expected')

else:

assert False

# Example 7

assert baz._MyParentObject__private_field == 71

# Example 8

print(baz.__dict__)

# Example 9

class MyClass(object):

def __init__(self, value):

self.__value = value

def get_value(self):

return str(self.__value)

foo = MyClass(5)

assert foo.get_value() == '5'

# Example 10

class MyIntegerSubclass(MyClass):

def get_value(self):

return int(self._MyClass__value)

foo = MyIntegerSubclass(5)

assert foo.get_value() == 5

# Example 11

class MyBaseClass(object):

def __init__(self, value):

self.__value = value

def get_value(self):

return self.__value

class MyClass(MyBaseClass):

def get_value(self):

return str(super().get_value())

class MyIntegerSubclass(MyClass):

def get_value(self):

return int(self._MyClass__value)

# Example 12

try:

foo = MyIntegerSubclass(5)

foo.get_value()

except:

logging.exception('Expected')

else:

assert False

# Example 13

class MyClass(object):

def __init__(self, value):

# This stores the user-supplied value for the object.

# It should be coercible to a string. Once assigned for

# the object it should be treated as immutable.

self._value = value

def get_value(self):

return str(self._value)

class MyIntegerSubclass(MyClass):

def get_value(self):

return self._value

foo = MyIntegerSubclass(5)

assert foo.get_value() == 5

# Example 14

class ApiClass(object):

def __init__(self):

self._value = 5

def get(self):

return self._value

class Child(ApiClass):

def __init__(self):

super().__init__()

self._value = 'hello' # Conflicts

a = Child()

print(a.get(), 'and', a._value, 'should be different')

# Example 15

class ApiClass(object):

def __init__(self):

self.__value = 5

def get(self):

return self.__value

class Child(ApiClass):

def __init__(self):

super().__init__()

self._value = 'hello' # OK!

a = Child()

print(a.get(), 'and', a._value, 'are different')

effectivepython/example_code/item_27.py at master · AISTLAB/effectivepython · GitHub

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