iframe-proxy | Sunbelt Computer Software

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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 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 MyObject:
    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
    foo.__private_field
    logging.exception('Expected')
    assert False
# Example 5
class MyOtherObject:
    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
    class MyParentObject:
        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()
    logging.exception('Expected')
    assert False
# Example 7
assert baz._MyParentObject__private_field == 71
# Example 8
print(baz.__dict__)
# Example 9
class MyStringClass:
    def __init__(self, value):
        self.__value = value
    def get_value(self):
        return str(self.__value)
foo = MyStringClass(5)
assert foo.get_value() == '5'
# Example 10
class MyIntegerSubclass(MyStringClass):
    def get_value(self):
        return int(self._MyStringClass__value)
foo = MyIntegerSubclass('5')
assert foo.get_value() == 5
# Example 11
class MyBaseClass:
    def __init__(self, value):
        self.__value = value
    def get_value(self):
        return self.__value
class MyStringClass(MyBaseClass):
    def get_value(self):
        return str(super().get_value())         # Updated
class MyIntegerSubclass(MyStringClass):
    def get_value(self):
        return int(self._MyStringClass__value)  # Not updated
# Example 12
    foo = MyIntegerSubclass(5)
    foo.get_value()
    logging.exception('Expected')
    assert False
# Example 13
class MyStringClass:
    def __init__(self, value):
        # This stores the user-supplied value for the object.
        # It should be coercible to a string. Once assigned in
        # the object it should be treated as immutable.
        self._value = value
    def get_value(self):
        return str(self._value)
class MyIntegerSubclass(MyStringClass):
    def get_value(self):
        return self._value
foo = MyIntegerSubclass(5)
assert foo.get_value() == 5
# Example 14
class ApiClass:
    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(f'{a.get()} and {a._value} should be different')
# Example 15
class ApiClass:
    def __init__(self):
        self.__value = 5       # Double underscore
    def get(self):
        return self.__value    # Double underscore
class Child(ApiClass):
    def __init__(self):
        super().__init__()
        self._value = 'hello'  # OK!
a = Child()
print(f'{a.get()} and {a._value} are different')
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