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item_042.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 42")
print("Example 1")
stock = {
"못": 125,
"나사못": 35,
"나비너트": 8,
"와셔": 24,
}
order = ["나사못", "나비너트", "클립"]
def get_batches(count, size):
return count // size
result = {}
for name in order:
count = stock.get(name, 0)
batches = get_batches(count, 8)
if batches:
result[name] = batches
print(result)
print("Example 2")
found = {name: get_batches(stock.get(name, 0), 8)
for name in order
if get_batches(stock.get(name, 0), 8)}
print(found)
print("Example 3")
has_bug = {name: get_batches(stock.get(name, 0), 4) # 틀림
for name in order
if get_batches(stock.get(name, 0), 8)}
print("원하는 답:", found)
print("실제 결과:", has_bug)
print("Example 4")
found = {name: batches for name in order
if (batches := get_batches(stock.get(name, 0), 8))}
assert found == {"나사못": 4, "나비너트": 1}, found
print("Example 5")
try:
result = {name: (tenth := count // 10)
for name, count in stock.items() if tenth > 0}
except:
logging.exception('이 예외가 발생해야 함')
else:
assert False
print("Example 6")
result = {name: tenth for name, count in stock.items()
if (tenth := count // 10) > 0}
print(result)
print("Example 7")
half = [(squared := last**2)
for count in stock.values()
if (last := count // 2) > 10]
print(f"{half}의 마지막 원소는 {last} ** 2 = {squared}")
print("Example 8")
for count in stock.values():
last = count // 2
squared = last**2
print(f"{count} // 2 = {last}; {last} ** 2 = {squared}")
print("Example 9")
try:
del count
half = [count // 2 for count in stock.values()]
print(half) # 작동함
print(count) # 루프 변수가 누출되지 않기 때문에 예외가 발생함
except:
logging.exception('이 예외가 발생해야 함')
else:
assert False
print("Example 10")
found = ((name, batches) for name in order
if (batches := get_batches(stock.get(name, 0), 8)))
print(next(found))
print(next(found))