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item_055.py
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#!/usr/bin/env PYTHONHASHSEED=1234 python3
# Copyright 2014-2024 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.
### 책 예제에 맞는 환경 설정을 시작함
import random
random.seed(1234)
import logging
from pprint import pprint
from sys import stdout as STDOUT
# 모든 출력을 임시 디렉터리로 보냄
import atexit
import gc
import io
import os
import tempfile
TEST_DIR = tempfile.TemporaryDirectory()
atexit.register(TEST_DIR.cleanup)
# 윈도우에서 프로세스가 제대로 종료되도록 함
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)
### 책 예제에 맞는 환경설정 끝
print("아이템 55")
print("Example 1")
class MyObject:
def __init__(self):
self.public_field = 5
self.__private_field = 10
def get_private_field(self):
return self.__private_field
print("Example 2")
foo = MyObject()
assert foo.public_field == 5
print("Example 3")
assert foo.get_private_field() == 10
print("Example 4")
try:
foo.__private_field
except:
logging.exception('이 예외가 발생해야 함')
else:
assert False
print("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
print("Example 6")
try:
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()
except:
logging.exception('이 예외가 발생해야 함')
else:
assert False
print("Example 7")
assert baz._MyParentObject__private_field == 71
print("Example 8")
print(baz.__dict__)
print("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"
print("Example 10")
class MyIntegerSubclass(MyStringClass):
def get_value(self):
return int(self._MyStringClass__value)
foo = MyIntegerSubclass("5")
assert foo.get_value() == 5
print("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
print("Example 12")
try:
foo = MyIntegerSubclass(5)
foo.get_value()
except:
logging.exception('이 예외가 발생해야 함')
else:
assert False
print("Example 13")
class MyStringClass:
def __init__(self, value):
# 여기서 객체에게 사용자가 제공한 값을 저장한다.
# 사용자가 제공하는 값은 문자열로 타입 변환이 가능해야 하며
# 일단 한번 객체 내부에 설정되고 나면 불변 값으로 취급돼야 한다.
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
print("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" # 충돌
a = Child()
print(f"{a.get()} 와 {a._value} 는 달라야만 한다")
print("Example 15")
class ApiClass:
def __init__(self):
self.__value = 5 # 밑줄 2개!
def get(self):
return self.__value # 밑줄 2개!
class Child(ApiClass):
def __init__(self):
super().__init__()
self._value = "hello" # 잘 됨!
a = Child()
print(f"{a.get()} 와 {a._value} 는 달라야만 한다")