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item_062.py
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executable file
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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 62")
print("Example 1")
class Meta(type):
def __new__(meta, name, bases, class_dict):
global print
orig_print = print
print(f"* {name}에 대해 {meta}.__new__ 실행")
print("부모클래스:", bases)
print = pprint
print(class_dict)
print = orig_print
return type.__new__(meta, name, bases, class_dict)
class MyClass(metaclass=Meta):
stuff = 123
def foo(self):
pass
class MySubclass(MyClass):
other = 567
def bar(self):
pass
print("Example 2")
class ValidatePolygon(type):
def __new__(meta, name, bases, class_dict):
# Polygon 클래스의 하위 클래스만 검증한다
if bases:
if class_dict["sides"] < 3:
raise ValueError("Polygon의 sides는 3 이상이어야 합니다")
return type.__new__(meta, name, bases, class_dict)
class Polygon(metaclass=ValidatePolygon):
sides = None # 하위 클래스가 이 값을 꼭 지정해야 함
@classmethod
def interior_angles(cls):
return (cls.sides - 2) * 180
class Triangle(Polygon):
sides = 3
class Rectangle(Polygon):
sides = 4
class Nonagon(Polygon):
sides = 9
assert Triangle.interior_angles() == 180
assert Rectangle.interior_angles() == 360
assert Nonagon.interior_angles() == 1260
print("Example 3")
try:
print("클래스 선언 이전")
class Line(Polygon):
print("sides 설정 이전")
sides = 2
print("sides 설정 이후")
print("클래스 선언 이후")
except:
logging.exception('이 예외가 발생해야 함')
else:
assert False
print("Example 4")
class BetterPolygon:
sides = None # Must be specified by subclasses
def __init_subclass__(cls):
super().__init_subclass__()
if cls.sides < 3:
raise ValueError("Polygon의 sides는 3 이상이어야 합니다")
@classmethod
def interior_angles(cls):
return (cls.sides - 2) * 180
class Hexagon(BetterPolygon):
sides = 6
assert Hexagon.interior_angles() == 720
print("Example 5")
try:
print("클래스 선언 이전")
class Point(BetterPolygon):
sides = 1
print("클래스 선언 이후")
except:
logging.exception('이 예외가 발생해야 함')
else:
assert False
print("Example 6")
class ValidateFilled(type):
def __new__(meta, name, bases, class_dict):
# Filled 클래스의 하위 클래스만 검증한다
if bases:
if class_dict["color"] not in ("red", "green"):
raise ValueError("지원하지 않는 채워 넣기 색상입니다")
return type.__new__(meta, name, bases, class_dict)
class Filled(metaclass=ValidateFilled):
color = None # 하위 클래스가 이 값을 꼭 지정해야 함
print("Example 7")
try:
class RedPentagon(Filled, Polygon):
color = "blue"
sides = 5
except:
logging.exception('이 예외가 발생해야 함')
else:
assert False
print("Example 8")
class ValidatePolygon(type):
def __new__(meta, name, bases, class_dict):
# 루트 클래스가 아닌 경우만 검증한다
if not class_dict.get("is_root"):
if class_dict["sides"] < 3:
raise ValueError("Polygon의 sides는 3 이상이어야 합니다")
return type.__new__(meta, name, bases, class_dict)
class Polygon(metaclass=ValidatePolygon):
is_root = True
sides = None # Must be specified by subclasses
class ValidateFilledPolygon(ValidatePolygon):
def __new__(meta, name, bases, class_dict):
# 루트 클래스가 아닌 경우만 검증한다
if not class_dict.get("is_root"):
if class_dict["color"] not in ("red", "green"):
raise ValueError("지원하지 않는 채워 넣기 색상입니다")
return super().__new__(meta, name, bases, class_dict)
class FilledPolygon(Polygon, metaclass=ValidateFilledPolygon):
is_root = True
color = None # 하위 클래스가 이 값을 꼭 지정해야 함
print("Example 9")
class GreenPentagon(FilledPolygon):
color = "green"
sides = 5
greenie = GreenPentagon()
assert isinstance(greenie, Polygon)
print("Example 10")
try:
class OrangePentagon(FilledPolygon):
color = "orange"
sides = 5
except:
logging.exception('이 예외가 발생해야 함')
else:
assert False
print("Example 11")
try:
class RedLine(FilledPolygon):
color = "red"
sides = 2
except:
logging.exception('이 예외가 발생해야 함')
else:
assert False
print("Example 12")
class Filled:
color = None # Must be specified by subclasses
def __init_subclass__(cls):
super().__init_subclass__()
if cls.color not in ("red", "green", "blue"):
raise ValueError("지원하지 않는 채워 넣기 색상입니다")
print("Example 13")
class RedTriangle(Filled, BetterPolygon):
color = "red"
sides = 3
ruddy = RedTriangle()
assert isinstance(ruddy, Filled)
assert isinstance(ruddy, BetterPolygon)
print("Example 14")
try:
print("클래스 선언 이전")
class BlueLine(Filled, BetterPolygon):
color = "blue"
sides = 2
print("클래스 선언 이후")
except:
logging.exception('이 예외가 발생해야 함')
else:
assert False
print("Example 15")
try:
print("클래스 선언 이전")
class BeigeSquare(Filled, BetterPolygon):
color = "beige"
sides = 4
print("클래스 선언 이후")
except:
logging.exception('이 예외가 발생해야 함')
else:
assert False
print("Example 16")
class Top:
def __init_subclass__(cls):
super().__init_subclass__()
print(f"{cls}의 Top")
class Left(Top):
def __init_subclass__(cls):
super().__init_subclass__()
print(f"{cls}의 Left")
class Right(Top):
def __init_subclass__(cls):
super().__init_subclass__()
print(f"{cls}의 Right")
class Bottom(Left, Right):
def __init_subclass__(cls):
super().__init_subclass__()
print(f"{cls}의 Bottom")