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item_048.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 48")
print("Example 1")
names = ["소크라테스", "아르키메데스", "플라톤", "아리스토텔레스"]
names.sort(key=len)
print(names)
print("Example 2")
def log_missing():
print("키가 추가됨")
return 0
print("Example 3")
from collections import defaultdict
current = {"초록": 12, "파랑": 3}
increments = [
("빨강", 5),
("파랑", 17),
("주황", 9),
]
result = defaultdict(log_missing, current)
print("이전:", dict(result))
for key, amount in increments:
result[key] += amount
print("이후:", dict(result))
print("Example 4")
def increment_with_report(current, increments):
added_count = 0
def missing():
nonlocal added_count # 상태가 있는 클로저
added_count += 1
return 0
result = defaultdict(missing, current)
for key, amount in increments:
result[key] += amount
return result, added_count
print("Example 5")
result, count = increment_with_report(current, increments)
assert count == 2
print(result)
print("Example 6")
class CountMissing:
def __init__(self):
self.added = 0
def missing(self):
self.added += 1
return 0
print("Example 7")
counter = CountMissing()
result = defaultdict(counter.missing, current) # 메서드 참조
for key, amount in increments:
result[key] += amount
assert counter.added == 2
print(result)
print("Example 8")
class BetterCountMissing:
def __init__(self):
self.added = 0
def __call__(self):
self.added += 1
return 0
counter = BetterCountMissing()
assert counter() == 0
assert callable(counter)
print("Example 9")
counter = BetterCountMissing()
result = defaultdict(counter, current) # __call__에 의존함
for key, amount in increments:
result[key] += amount
assert counter.added == 2
print(result)