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item_16.py
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executable file
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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 gc
import io
import os
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
counters = {
'pumpernickel': 2,
'sourdough': 1,
}
# Example 2
key = 'wheat'
if key in counters:
count = counters[key]
else:
count = 0
counters[key] = count + 1
print(counters)
# Example 3
key = 'brioche'
try:
count = counters[key]
except KeyError:
count = 0
counters[key] = count + 1
print(counters)
# Example 4
key = 'multigrain'
count = counters.get(key, 0)
counters[key] = count + 1
print(counters)
# Example 5
key = 'baguette'
if key not in counters:
counters[key] = 0
counters[key] += 1
key = 'ciabatta'
if key in counters:
counters[key] += 1
else:
counters[key] = 1
key = 'ciabatta'
try:
counters[key] += 1
except KeyError:
counters[key] = 1
print(counters)
# Example 6
votes = {
'baguette': ['Bob', 'Alice'],
'ciabatta': ['Coco', 'Deb'],
}
key = 'brioche'
who = 'Elmer'
if key in votes:
names = votes[key]
else:
votes[key] = names = []
names.append(who)
print(votes)
# Example 7
key = 'rye'
who = 'Felix'
try:
names = votes[key]
except KeyError:
votes[key] = names = []
names.append(who)
print(votes)
# Example 8
key = 'wheat'
who = 'Gertrude'
names = votes.get(key)
if names is None:
votes[key] = names = []
names.append(who)
print(votes)
# Example 9
key = 'brioche'
who = 'Hugh'
if (names := votes.get(key)) is None:
votes[key] = names = []
names.append(who)
print(votes)
# Example 10
key = 'cornbread'
who = 'Kirk'
names = votes.setdefault(key, [])
names.append(who)
print(votes)
# setdefault는 dict에서 key를 사용해 값을 가져오려고 시도하고
# key가 없으면 default 값을 설정하고 반환한다
# Example 11
data = {}
key = 'foo'
value = []
data.setdefault(key, value)
print('Before:', data)
value.append('hello')
print('After: ', data)
# key가 없으면 setdefault에 전달된 디폴트 값이 별도로 복사되지 않고 딕셔너리에 직접 대입된다
# key에 해당하는 default 값을 setdefault에 전달할 때마다 그 값을 새로 만들어야한다는 뜻
# 호출할 때마다 리스트를 만들어야하므로 성능 저하될 수 있다
# Example 12
key = 'dutch crunch'
count = counters.setdefault(key, 0) # 여기서 setdefault 굳이 호출할 필요 없다 get 사용
counters[key] = count + 1
print(counters)
# 문제에 dict의 setdefault 메섣 사용 방법이 가장 적합해보인다면
# setdefault 대신 defaultdict 사용 고려해보자