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item_11.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
a = ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h']
print('Middle two: ', a[3:5])
print('All but ends:', a[1:7])
# Example 2
assert a[:5] == a[0:5]
# Example 3
assert a[5:] == a[5:len(a)]
# Example 4
print(a[:])
print(a[:5])
print(a[:-1])
print(a[4:])
print(a[-3:])
print(a[2:5])
print(a[2:-1])
print(a[-3:-1])
# Example 5
a[:] # ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h']
a[:5] # ['a', 'b', 'c', 'd', 'e']
a[:-1] # ['a', 'b', 'c', 'd', 'e', 'f', 'g']
a[4:] # ['e', 'f', 'g', 'h']
a[-3:] # ['f', 'g', 'h']
a[2:5] # ['c', 'd', 'e']
a[2:-1] # ['c', 'd', 'e', 'f', 'g']
a[-3:-1] # ['f', 'g']
# Example 6
first_twenty_items = a[:20]
last_twenty_items = a[-20:]
# Example 7
try:
a[20]
except:
logging.exception('Expected')
else:
assert False
# Example 8
b = a[3:]
print('Before: ', b)
b[1] = 99
print('After: ', b)
print('No change:', a)
# 리스트 슬라이싱한 결과는 완전히 새로운 리스트
# 원래 리스트에 대한 참조는 그대로 유지
# 슬라이싱 리스트 변경해도 원래 리스트는 바꾸지 않음
# Example 9
print('Before ', a)
a[2:7] = [99, 22, 14] # 슬라이스 대입
print('After ', a)
# Example 10
print('Before ', a)
a[2:3] = [47, 11] # 슬라이스 대입에서는 언패킹 대입 (e.g. a, b = c[:2])과 달리 길이 같을 필요 X
print('After ', a)
# Example 11
b = a[:] # 원래 리스트 복사한 새 리스트
assert b == a and b is not a
# Example 12
b = a
print('Before a', a)
print('Before b', b)
a[:] = [101, 102, 103]
assert a is b # Still the same list object
print('After a ', a) # Now has different contents
print('After b ', b) # Same list, so same contents as a (같은 리스트 객체라서 a와 내용이 같음)